Six degree-of-freedom laser tracker that cooperates with a remote projector to convey information

ABSTRACT

A method of conveying information to a user of a coordinate measurement device, includes providing a first target projector, sending a first light beam from the device to a retroreflector; receiving a second light beam from the retroreflector; measuring the orientational and translational sets, the translational set based on the second light beam; selecting first information to be conveyed from the group consisting of one or more positions on the object, a direction indicated by a moving pattern, a message that includes one or more symbols or alphanumeric characters, a hidden feature, a measured object characteristic, a modeled characteristic, a magnified representation of surface characteristics, a pattern having meaning according to a rule, and combinations thereof; determining a first light pattern corresponding to the information; storing the first light pattern; and projecting the first light pattern onto the object based on the translational and orientational sets.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of U.S. Provisional PatentApplication No. 61/592,049 filed Jan. 30, 2012, and U.S. ProvisionalPatent Application No. 61/475,703 filed Apr. 15, 2011, the entirecontents of both of which are hereby incorporated by reference.

BACKGROUND

The present disclosure relates to a coordinate measuring device. One setof coordinate measurement devices belongs to a class of instruments thatmeasure the three-dimensional (3D) coordinates of a point by sending alaser beam to the point. The laser beam may impinge directly on thepoint or on a retroreflector target in contact with the point. In eithercase, the instrument determines the coordinates of the point bymeasuring the distance and the two angles to the target. The distance ismeasured with a distance-measuring device such as an absolute distancemeter or an interferometer. The angles are measured with anangle-measuring device such as an angular encoder. A gimbaledbeam-steering mechanism within the instrument directs the laser beam tothe point of interest.

The laser tracker is a particular type of coordinate-measuring devicethat tracks the retroreflector target with one or more laser beams itemits. Coordinate-measuring devices closely related to the laser trackerare the laser scanner and the total station. The laser scanner steps oneor more laser beams to points on a surface. It picks up light scatteredfrom the surface and from this light determines the distance and twoangles to each point. The total station, which is most often used insurveying applications, may be used to measure the coordinates ofdiffusely scattering or retroreflective targets. Hereinafter, the termlaser tracker is used in a broad sense to include laser scanners andtotal stations.

Ordinarily the laser tracker sends a laser beam to a retroreflectortarget. A common type of retroreflector target is the sphericallymounted retroreflector (SMR), which comprises a cube-cornerretroreflector embedded within a metal sphere. The cube-cornerretroreflector comprises three mutually perpendicular mirrors. Thevertex, which is the common point of intersection of the three mirrors,is located at the center of the sphere. Because of this placement of thecube corner within the sphere, the perpendicular distance from thevertex to any surface on which the SMR rests remains constant, even asthe SMR is rotated. Consequently, the laser tracker can measure the 3Dcoordinates of a surface by following the position of an SMR as it ismoved over the surface. Stating this another way, the laser trackerneeds to measure only three degrees of freedom (one radial distance andtwo angles) to fully characterize the 3D coordinates of a surface.

One type of laser tracker contains only an interferometer (IFM) withoutan absolute distance meter (ADM). If an object blocks the path of thelaser beam from one of these trackers, the IFM loses its distancereference. The operator must then track the retroreflector to a knownlocation to reset to a reference distance before continuing themeasurement. A way around this limitation is to put an ADM in thetracker. The ADM can measure distance in a point-and-shoot manner, asdescribed in more detail below. Some laser trackers contain only an ADMwithout an interferometer. U.S. Pat. No. 7,352,446 ('446) to Bridges etal., the contents of which are herein incorporated by reference,describes a laser tracker having only an ADM (and no IFM) that is ableto accurately scan a moving target. Prior to the '446 patent, absolutedistance meters were too slow to accurately find the position of amoving target.

A gimbal mechanism within the laser tracker may be used to direct alaser beam from the tracker to the SMR. Part of the light retroreflectedby the SMR enters the laser tracker and passes onto a position detector.A control system within the laser tracker can use the position of thelight on the position detector to adjust the rotation angles of themechanical axes of the laser tracker to keep the laser beam centered onthe SMR. In this way, the tracker is able to follow (track) an SMR thatis moved over the surface of an object of interest.

Angle measuring devices such as angular encoders are attached to themechanical axes of the tracker. The one distance measurement and twoangle measurements performed by the laser tracker are sufficient tocompletely specify the three-dimensional location of the SMR.

Several laser trackers are available or have been proposed for measuringsix, rather than the ordinary three, degrees of freedom. Exemplary sixdegree-of-freedom (six-DOF) systems are described by U.S. Pat. No.7,800,758 (758) to Bridges et al., the contents of which are hereinincorporated by reference, and U.S. Published Patent Application2010/0128259 to Bridges et al., the contents of which are hereinincorporated by reference.

There is a need for new types of six-DOF accessories that provide a widevariety of capabilities when used with six-DOF laser trackers.

SUMMARY

According to an embodiment of the present invention, a method ofmeasuring three or more surface sets on an object surface with acoordinate measurement device and a target scanner, each of the three ofmore surface sets being three-dimensional coordinates of a point on theobject surface in a device frame of reference, each surface setincluding three values, the device frame of reference being associatedwith the coordinate measurement device. The method includes the stepsof: providing the target scanner having a body, a first retroreflector,a projector, a camera, and a scanner processor, wherein the firstretroreflector, projector, and camera are rigidly affixed to the body,and the target scanner is mechanically detached to the coordinatemeasurement device, wherein the projector includes a source pattern oflight and a projector lens, the source pattern of light located on asource plane and including at least three non-collinear patternelements, the projector lens configured to project the source pattern oflight onto the object to form an object pattern of light on the object,each of the at least three non-collinear pattern elements correspondingto at least one surface set, wherein the camera includes a camera lensand a photosensitive array, the camera lens configured to image theobject pattern of light onto the photosensitive array as an imagepattern of light, the photosensitive array including camera pixels, thephotosensitive array configured to produce, for each camera pixel, acorresponding pixel digital value responsive to an amount of lightreceived by the camera pixel from the image pattern of light. The methodalso includes: providing the coordinate measurement device, thecoordinate measurement device configured to measure a translational setand an orientational set, the translational set being values of threetranslational degrees of freedom of the target scanner in the deviceframe of reference and the orientational set being values of threeorientational degrees of freedom of the target scanner in the deviceframe of reference, the translational set and the orientational setbeing sufficient to define a position and orientation of the targetscanner in space, the coordinate measurement device configured to send afirst beam of light to the first retroreflector and to receive a secondbeam of light from the first retroreflector, the second beam of lightbeing a portion of the first beam of light, the coordinate measurementdevice including a device processor, the device processor configured todetermine the orientational set and the translational set, thetranslation set based at least in part on the second beam of light,wherein the scanner processor and the device processor are jointlyconfigured to determine the three or more surface sets, each of thesurface sets based at least in part on the translational set, theorientational set, and the pixel digital values. The method furtherincludes: selecting the source pattern of light; projecting the sourcepattern of light onto the object to produce the object pattern of light;imaging the object pattern of light onto the photosensitive array toobtain the image pattern of light; obtaining the pixel digital valuesfor the image pattern of light; sending the first beam of light from thecoordinate measurement device to the first retroreflector; receiving thesecond beam of light from the first retroreflector; measuring thetranslational set and the orientational set with the coordinatemeasurement device based at least in part on the second beam of light;determining the surface sets corresponding to each of the at least threenon-collinear pattern elements; and saving the surface sets.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings, exemplary embodiments are shown whichshould not be construed to be limiting regarding the entire scope of thedisclosure, and wherein the elements are numbered alike in severalFIGURES:

FIG. 1 is a perspective view of a laser tracker system with aretroreflector target in accordance with an embodiment of the presentinvention;

FIG. 2 is a perspective view of a laser tracker system with a six-DOFtarget in accordance with an embodiment of the present invention;

FIG. 3 is a block diagram describing elements of laser tracker opticsand electronics in accordance with an embodiment of the presentinvention;

FIG. 4, which includes FIGS. 4A and 4B, shows two types of prior artafocal beam expanders;

FIG. 5 shows a prior art fiber-optic beam launch;

FIG. 6A-D are schematic figures that show four types of prior artposition detector assemblies;

FIGS. 6E and 6F are schematic figures showing position detectorassemblies according to embodiments of the present invention;

FIG. 7 is a block diagram of electrical and electro-optical elementswithin a prior art ADM;

FIGS. 8A and 8B are schematic figures showing fiber-optic elementswithin a prior art fiber-optic network;

FIG. 8C is a schematic figure showing fiber-optic elements within afiber-optic network in accordance with an embodiment of the presentinvention;

FIG. 9 is an exploded view of a prior art laser tracker;

FIG. 10 is a cross-sectional view of a prior art laser tracker;

FIG. 11 is a block diagram of the computing and communication elementsof a laser tracker in accordance with an embodiment of the presentinvention;

FIG. 12A is a block diagram of elements in a laser tracker that uses asingle wavelength according to an embodiment of the present invention;

FIG. 12B is a block diagram of elements in a laser tracker that uses asingle wavelength according to an embodiment of the present invention;

FIG. 13 is a block diagram of elements in a laser tracker with six-DOFcapability according to an embodiment of the present invention;

FIG. 14 are block diagrams of elements in a laser tracker having six-DOFcapability according to an embodiment of the present invention;

FIGS. 15 and 15C are block diagrams of elements in a laser trackerhaving six-DOF capability according to an embodiment of the presentinvention;

FIGS. 15A, 15B, 15D, and 15E are schematic representations illustratingthe principles of operation of triangulation based scanning measurementsystems;

FIG. 15F illustrates steps that can be taken according to an embodimentof the present invention to ensure high quality measurement results;

FIGS. 16, 16A, and 16B are schematic diagrams showing elements of asix-DOF indicator according to an embodiment of the present invention;

FIG. 17 is a block diagram of a six-DOF projector in accordance with anembodiment of the present invention;

FIG. 18 is a block diagram of a six-DOF projector in accordance with anembodiment of the present invention;

FIG. 19 is a block diagram of a six-DOF sensor in accordance with anembodiment of the present invention;

FIG. 19A is a block diagram of a six-DOF sensor in accordance with anembodiment of the present invention;

FIG. 20 is a flowchart of steps in a method of measuring three or moresurface sets on an object surface with a coordinate measurement deviceand a target scanner according to an embodiment of the presentinvention;

FIG. 21 is a flowchart of steps in a method that follows on marker A inFIG. 20;

FIG. 22 is a flowchart of steps in a method that follows on marker A inFIG. 20;

FIG. 23 is a flowchart of steps in a method that follows on marker A inFIG. 20;

FIG. 24 is a flowchart of steps in a method of measuring with acoordinate measurement device and a target sensor a sense characteristicand a surface set associated with the sense characteristic according toan embodiment of the present invention;

FIG. 25 is a flowchart of steps in a method that follows on marker B inFIG. 24;

FIG. 26 is a flowchart of steps in a method of conveying firstinformation to a user of a coordinate measurement device by projecting afirst pattern with a first target projector according to an embodimentof the present invention;

FIG. 27 is a flowchart of steps in a method that follows on marker C inFIG. 26;

FIG. 28 is a flowchart of steps in a method that follows on marker C inFIG. 26;

FIG. 29 is a flowchart of steps in a method that follows on marker C inFIG. 26;

FIG. 30 is a flowchart of steps in a method that follows on marker C inFIG. 26;

FIG. 31 is a flowchart of steps in a method to measure a plurality ofsurface sets on an object surface with a coordinate measurement deviceand a target scanner according to an embodiment of the presentinvention; and

FIG. 32 is a flowchart of steps in a method to measure a plurality ofsurface sets on an object surface with a coordinate measurement deviceand a target scanner according to an embodiment of the presentinvention.

DETAILED DESCRIPTION

An exemplary laser tracker system 5 illustrated in FIG. 1 includes alaser tracker 10, a retroreflector target 26, an optional auxiliary unitprocessor 50, and an optional auxiliary computer 60. An exemplarygimbaled beam-steering mechanism 12 of laser tracker 10 comprises azenith carriage 14 mounted on an azimuth base 16 and rotated about anazimuth axis 20. A payload 15 is mounted on the zenith carriage 14 androtated about a zenith axis 18. Zenith axis 18 and azimuth axis 20intersect orthogonally, internally to tracker 10, at gimbal point 22,which is typically the origin for distance measurements. A laser beam 46virtually passes through the gimbal point 22 and is pointed orthogonalto zenith axis 18. In other words, laser beam 46 lies in a planeapproximately perpendicular to the zenith axis 18 and that passesthrough the azimuth axis 20. Outgoing laser beam 46 is pointed in thedesired direction by rotation of payload 15 about zenith axis 18 and byrotation of zenith carriage 14 about azimuth axis 20. A zenith angularencoder, internal to the tracker, is attached to a zenith mechanicalaxis aligned to the zenith axis 18. An azimuth angular encoder, internalto the tracker, is attached to an azimuth mechanical axis aligned to theazimuth axis 20. The zenith and azimuth angular encoders measure thezenith and azimuth angles of rotation to relatively high accuracy.Outgoing laser beam 46 travels to the retroreflector target 26, whichmight be, for example, a spherically mounted retroreflector (SMR) asdescribed above. By measuring the radial distance between gimbal point22 and retroreflector 26, the rotation angle about the zenith axis 18,and the rotation angle about the azimuth axis 20, the position ofretroreflector 26 is found within the spherical coordinate system of thetracker.

Outgoing laser beam 46 may include one or more laser wavelengths, asdescribed hereinafter. For the sake of clarity and simplicity, asteering mechanism of the sort shown in FIG. 1 is assumed in thefollowing discussion. However, other types of steering mechanisms arepossible. For example, it is possible to reflect a laser beam off amirror rotated about the azimuth and zenith axes. The techniquesdescribed herein are applicable, regardless of the type of steeringmechanism.

Magnetic nests 17 may be included on the laser tracker for resetting thelaser tracker to a “home” position for different sized SMRs—for example,1.5, ⅞, and ½ inch SMRs. An on-tracker retroreflector 19 may be used toreset the tracker to a reference distance. In addition, an on-trackermirror, not visible from the view of FIG. 1, may be used in combinationwith the on-tracker retroreflector to enable performance of aself-compensation, as described in U.S. Pat. No. 7,327,446, the contentsof which are incorporated by reference.

FIG. 2 shows an exemplary laser tracker system 7 that is like the lasertracker system 5 of FIG. 1 except that retroreflector target 26 isreplaced with a six-DOF probe 1000. In FIG. 1, other types ofretroreflector targets may be used. For example, a cateyeretroreflector, which is a glass retroreflector in which light focusesto a small spot of light on a reflective rear surface of the glassstructure, is sometimes used.

FIG. 3 is a block diagram showing optical and electrical elements in alaser tracker embodiment. It shows elements of a laser tracker that emittwo wavelengths of light—a first wavelength for an ADM and a secondwavelength for a visible pointer and for tracking. The visible pointerenables the user to see the position of the laser beam spot emitted bythe tracker. The two different wavelengths are combined using afree-space beam splitter. Electrooptic (EO) system 100 includes visiblelight source 110, isolator 115, optional first fiber launch 170,optional interferometer (IFM) 120, beam expander 140, first beamsplitter 145, position detector assembly 150, second beam splitter 155,ADM 160, and second fiber launch 170.

Visible light source 110 may be a laser, superluminescent diode, orother light emitting device. The isolator 115 may be a Faraday isolator,attenuator, or other device capable of reducing the light that reflectsback into the light source. Optional IFM may be configured in a varietyof ways. As a specific example of a possible implementation, the IFM mayinclude a beam splitter 122, a retroreflector 126, quarter waveplates124, 130, and a phase analyzer 128. The visible light source 110 maylaunch the light into free space, the light then traveling in free spacethrough the isolator 115, and optional IFM 120. Alternatively, theisolator 115 may be coupled to the visible light source 110 by a fiberoptic cable. In this case, the light from the isolator may be launchedinto free space through the first fiber-optic launch 170, as discussedherein below with reference to FIG. 5.

Beam expander 140 may be set up using a variety of lens configurations,but two commonly used prior-art configurations are shown in FIGS. 4A,4B. FIG. 4A shows a configuration 140A based on the use of a negativelens 141A and a positive lens 142A. A beam of collimated light 220Aincident on the negative lens 141A emerges from the positive lens 142Aas a larger beam of collimated light 230A. FIG. 4B shows a configuration140B based on the use of two positive lenses 141B, 142B. A beam ofcollimated light 220B incident on a first positive lens 141B emergesfrom a second positive lens 142B as a larger beam of collimated light230B. Of the light leaving the beam expander 140, a small amountreflects off the beam splitters 145, 155 on the way out of the trackerand is lost. That part of the light that passes through the beamsplitter 155 is combined with light from the ADM 160 to form a compositebeam of light 188 that leaves that laser tracker and travels to theretroreflector 90.

In an embodiment, the ADM 160 includes a light source 162, ADMelectronics 164, a fiber network 166, an interconnecting electricalcable 165, and interconnecting optical fibers 168, 169, 184, 186. ADMelectronics send electrical modulation and bias voltages to light source162, which may, for example, be a distributed feedback laser thatoperates at a wavelength of approximately 1550 nm. In an embodiment, thefiber network 166 may be the prior art fiber-optic network 420A shown inFIG. 8A. In this embodiment, light from the light source 162 in FIG. 3travels over the optical fiber 184, which is equivalent to the opticalfiber 432 in FIG. 8A.

The fiber network of FIG. 8A includes a first fiber coupler 430, asecond fiber coupler 436, and low-transmission reflectors 435, 440. Thelight travels through the first fiber coupler 430 and splits between twopaths, the first path through optical fiber 433 to the second fibercoupler 436 and the second path through optical fiber 422 and fiberlength equalizer 423. Fiber length equalizer 423 connects to fiberlength 168 in FIG. 3, which travels to the reference channel of the ADMelectronics 164. The purpose of fiber length equalizer 423 is to matchthe length of optical fibers traversed by light in the reference channelto the length of optical fibers traversed by light in the measurechannel. Matching the fiber lengths in this way reduces ADM errorscaused by changes in the ambient temperature. Such errors may arisebecause the effective optical path length of an optical fiber is equalto the average index of refraction of the optical fiber times the lengthof the fiber. Since the index of refraction of the optical fibersdepends on the temperature of the fiber, a change in the temperature ofthe optical fibers causes changes in the effective optical path lengthsof the measure and reference channels. If the effective optical pathlength of the optical fiber in the measure channel changes relative tothe effective optical path length of the optical fiber in the referencechannel, the result will be an apparent shift in the position of theretroreflector target 90, even if the retroreflector target 90 is keptstationary. To get around this problem, two steps are taken. First, thelength of the fiber in the reference channel is matched, as nearly aspossible, to the length of the fiber in the measure channel. Second, themeasure and reference fibers are routed side by side to the extentpossible to ensure that the optical fibers in the two channels seenearly the same changes in temperature.

The light travels through the second fiber optic coupler 436 and splitsinto two paths, the first path to the low-reflection fiber terminator440 and the second path to optical fiber 438, from which it travels tooptical fiber 186 in FIG. 3. The light on optical fiber 186 travelsthrough to the second fiber launch 170.

In an embodiment, fiber launch 170 is shown in prior art FIG. 5. Thelight from optical fiber 186 of FIG. 3 goes to fiber 172 in FIG. 5. Thefiber launch 170 includes optical fiber 172, ferrule 174, and lens 176.The optical fiber 172 is attached to ferrule 174, which is stablyattached to a structure within the laser tracker 10. If desired, the endof the optical fiber may be polished at an angle to reduce backreflections. The light 250 emerges from the core of the fiber, which maybe a single mode optical fiber with a diameter of between 4 and 12micrometers, depending on the wavelength of the light being used and theparticular type of optical fiber. The light 250 diverges at an angle andintercepts lens 176, which collimates it. The method of launching andreceiving an optical signal through a single optical fiber in an ADMsystem was described in reference to FIG. 3 in patent '758.

Referring to FIG. 3, the beam splitter 155 may be a dichroic beamsplitter, which transmits different wavelengths than it reflects. In anembodiment, the light from the ADM 160 reflects off dichroic beamsplitter 155 and combines with the light from the visible laser 110,which is transmitted through the dichroic beam splitter 155. Thecomposite beam of light 188 travels out of the laser tracker toretroreflector 90 as a first beam, which returns a portion of the lightas a second beam. That portion of the second beam that is at the ADMwavelength reflects off the dichroic beam splitter 155 and returns tothe second fiber launch 170, which couples the light back into theoptical fiber 186.

In an embodiment, the optical fiber 186 corresponds to the optical fiber438 in FIG. 8A. The returning light travels from optical fiber 438through the second fiber coupler 436 and splits between two paths. Afirst path leads to optical fiber 424 that, in an embodiment,corresponds to optical fiber 169 that leads to the measure channel ofthe ADM electronics 164 in FIG. 3. A second path leads to optical fiber433 and then to the first fiber coupler 430. The light leaving the firstfiber coupler 430 splits between two paths, a first path to the opticalfiber 432 and a second path to the low reflectance termination 435. Inan embodiment, optical fiber 432 corresponds to the optical fiber 184,which leads to the light source 162 in FIG. 3. In most cases, the lightsource 162 contains a built-in Faraday isolator that minimizes theamount of light that enters the light source from optical fiber 432.Excessive light fed into a laser in the reverse direction candestabilize the laser.

The light from the fiber network 166 enters ADM electronics 164 throughoptical fibers 168, 169. An embodiment of prior art ADM electronics isshown in FIG. 7. Optical fiber 168 in FIG. 3 corresponds to opticalfiber 3232 in FIG. 7, and optical fiber 169 in FIG. 3 corresponds tooptical fiber 3230 in FIG. 7. Referring now to FIG. 7, ADM electronics3300 includes a frequency reference 3302, a synthesizer 3304, a measuredetector 3306, a reference detector 3308, a measure mixer 3310, areference mixer 3312, conditioning electronics 3314, 3316, 3318, 3320, adivide-by-N prescaler 3324, and an analog-to-digital converter (ADC)3322. The frequency reference, which might be an oven-controlled crystaloscillator (OCXO), for example, sends a reference frequency f_(REF),which might be 10 MHz, for example, to the synthesizer, which generatestwo electrical signals—one signal at a frequency f_(RF) and two signalsat frequency f_(LO). The signal f_(RF) goes to the light source 3102,which corresponds to the light source 162 in FIG. 3. The two signals atfrequency f_(LO) go to the measure mixer 3310 and the reference mixer3312. The light from optical fibers 168, 169 in FIG. 3 appear on fibers3232, 3230 in FIG. 7, respectively, and enter the reference and measurechannels, respectively. Reference detector 3308 and measure detector3306 convert the optical signals into electrical signals. These signalsare conditioned by electrical components 3316, 3314, respectively, andare sent to mixers 3312, 3310, respectively. The mixers produce afrequency f_(IF) equal to the absolute value of f_(LO)−f_(RF). Thesignal f_(RF) may be a relatively high frequency, for example, 2 GHz,while the signal f_(IF) may have a relatively low frequency, forexample, 10 kHz.

The reference frequency f_(REF) is sent to the prescaler 3324, whichdivides the frequency by an integer value. For example, a frequency of10 MHz might be divided by 40 to obtain an output frequency of 250 kHz.In this example, the 10 kHz signals entering the ADC 3322 would besampled at a rate of 250 kHz, thereby producing 25 samples per cycle.The signals from the ADC 3322 are sent to a data processor 3400, whichmight, for example, be one or more digital signal processor (DSP) unitslocated in ADM electronics 164 of FIG. 3.

The method for extracting a distance is based on the calculation ofphase of the ADC signals for the reference and measure channels. Thismethod is described in detail in U.S. Pat. No. 7,701,559 ('559) toBridges et al., the contents of which are herein incorporated byreference. Calculation includes use of equations (1)-(8) of patent '559.In addition, when the ADM first begins to measure a retroreflector, thefrequencies generated by the synthesizer are changed some number oftimes (for example, three times), and the possible ADM distancescalculated in each case. By comparing the possible ADM distances foreach of the selected frequencies, an ambiguity in the ADM measurement isremoved. The equations (1)-(8) of patent '559 combined withsynchronization methods described with respect to FIG. 5 of patent '559and the Kalman filter methods described in patent '559 enable the ADM tomeasure a moving target. In other embodiments, other methods ofobtaining absolute distance measurements, for example, by using pulsedtime-of-flight rather than phase differences, may be used.

The part of the return light beam 190 that passes through the beamsplitter 155 arrives at the beam splitter 145, which sends part of thelight to the beam expander 140 and another part of the light to theposition detector assembly 150. The light emerging from the lasertracker 10 or EO system 100 may be thought of as a first beam and theportion of that light reflecting off the retroreflector 90 or 26 as asecond beam. Portions of the reflected beam are sent to differentfunctional elements of the EO system 100. For example, a first portionmay be sent to a distance meter such as an ADM 160 in FIG. 3. A secondportion may be sent to a position detector assembly 150. In some cases,a third portion may be sent to other functional units such as anoptional interferometer 120. It is important to understand that,although, in the example of FIG. 3, the first portion and the secondportion of the second beam are sent to the distance meter and theposition detector after reflecting off beam splitters 155 and 145,respectively, it would have been possible to transmit, rather thanreflect, the light onto a distance meter or position detector.

Four examples of prior art position detector assemblies 150A-150D areshown in FIGS. 6A-D. FIG. 6A depicts the simplest implementation, withthe position detector assembly including a position sensor 151 mountedon a circuit board 152 that obtains power from and returns signals toelectronics box 350, which may represent electronic processingcapability at any location within the laser tracker 10, auxiliary unit50, or external computer 60. FIG. 6B includes an optical filter 154 thatblocks unwanted optical wavelengths from reaching the position sensor151. The unwanted optical wavelengths may also be blocked, for example,by coating the beam splitter 145 or the surface of the position sensor151 with an appropriate film. FIG. 6C includes a lens 153 that reducesthe size of the beam of light. FIG. 6D includes both an optical filter154 and a lens 153.

FIG. 6E shows a novel position detector assembly that includes anoptical conditioner 149E. Optical conditioner contains a lens 153 andmay also contain optional wavelength filter 154. In addition, itincludes at least one of a diffuser 156 and a spatial filter 157. Asexplained hereinabove, a popular type of retroreflector is thecube-corner retroreflector. One type of cube corner retroreflector ismade of three mirrors, each joined at right angles to the other twomirrors. Lines of intersection at which these three mirrors are joinedmay have a finite thickness in which light is not perfectly reflectedback to the tracker. The lines of finite thickness are diffracted asthey propagate so that upon reaching the position detector they may notappear exactly the same as at the position detector. However, thediffracted light pattern will generally depart from perfect symmetry. Asa result, the light that strikes the position detector 151 may have, forexample, dips or rises in optical power (hot spots) in the vicinity ofthe diffracted lines. Because the uniformity of the light from theretroreflector may vary from retroreflector to retroreflector and alsobecause the distribution of light on the position detector may vary asthe retroreflector is rotated or tilted, it may be advantageous toinclude a diffuser 156 to improve the smoothness of the light thatstrikes the position detector 151. It might be argued that, because anideal position detector should respond to a centroid and an idealdiffuser should spread a spot symmetrically, there should be no effecton the resulting position given by the position detector. However, inpractice the diffuser is observed to improve performance of the positiondetector assembly, probably because the effects of nonlinearities(imperfections) in the position detector 151 and the lens 153. Cubecorner retroreflectors made of glass may also produce non-uniform spotsof light at the position detector 151. Variations in a spot of light ata position detector may be particularly prominent from light reflectedfrom cube corners in six-DOF targets, as may be understood more clearlyfrom commonly assigned U.S. patent application Ser. Nos. 13/370,339filed Feb. 10, 2012, and 13/407,983, filed Feb. 29, 2012, the contentsof which are incorporated by reference. In an embodiment, the diffuser156 is a holographic diffuser. A holographic diffuser providescontrolled, homogeneous light over a specified diffusing angle. In otherembodiments, other types of diffusers such as ground glass or “opal”diffusers are used.

The purpose of the spatial filter 157 of the position detector assembly150E is to block ghost beams that may be the result, for example, ofunwanted reflections off optical surfaces, from striking the positiondetector 151. A spatial filter includes a plate 157 that has anaperture. By placing the spatial filter 157 a distance away from thelens equal approximately to the focal length of the lens, the returninglight 243E passes through the spatial filter when it is near itsnarrowest—at the waist of the beam. Beams that are traveling at adifferent angle, for example, as a result of reflection of an opticalelement strike the spatial filter away from the aperture and are blockedfrom reaching the position detector 151. An example is shown in FIG. 6E,where an unwanted ghost beam 244E reflects off a surface of the beamsplitter 145 and travels to spatial filter 157, where it is blocked.Without the spatial filter, the ghost beam 244E would have interceptedthe position detector 151, thereby causing the position of the beam 243Eon the position detector 151 to be incorrectly determined. Even a weakghost beam may significantly change the position of the centroid on theposition detector 151 if the ghost beam is located a relatively largedistance from the main spot of light.

A retroreflector of the sort discussed here, a cube corner or a cateyeretroreflector, for example, has the property of reflecting a ray oflight that enters the retroreflector in a direction parallel to theincident ray. In addition, the incident and reflected rays aresymmetrically placed about the point of symmetry of the retroreflector.For example, in an open-air cube corner retroreflector, the point ofsymmetry of the retroreflector is the vertex of the cube corner. In aglass cube corner retroreflector, the point of symmetry is also thevertex, but one must consider the bending of the light at the glass-airinterface in this case. In a cateye retroreflector having an index ofrefraction of 2.0, the point of symmetry is the center of the sphere. Ina cateye retroreflector made of two glass hemispheres symmetricallyseated on a common plane, the point of symmetry is a point lying on theplane and at the spherical center of each hemisphere. The main point isthat, for the type of retroreflectors ordinarily used with lasertrackers, the light returned by a retroreflector to the tracker isshifted to the other side of the vertex relative to the incident laserbeam.

This behavior of a retroreflector 90 in FIG. 3 is the basis for thetracking of the retroreflector by the laser tracker. The position sensorhas on its surface an ideal retrace point. The ideal retrace point isthe point at which a laser beam sent to the point of symmetry of aretroreflector (e.g., the vertex of the cube corner retroreflector in anSMR) will return. Usually the retrace point is near the center of theposition sensor. If the laser beam is sent to one side of theretroreflector, it reflects back on the other side and appears off theretrace point on the position sensor. By noting the position of thereturning beam of light on the position sensor, the control system ofthe laser tracker 10 can cause the motors to move the light beam towardthe point of symmetry of the retroreflector.

If the retroreflector is moved transverse to the tracker at a constantvelocity, the light beam at the retroreflector will strike theretroreflector (after transients have settled) a fixed offset distancefrom the point of symmetry of the retroreflector. The laser trackermakes a correction to account for this offset distance at theretroreflector based on scale factor obtained from controlledmeasurements and based on the distance from the light beam on theposition sensor to the ideal retrace point.

As explained hereinabove, the position detector performs two importantfunctions—enabling tracking and correcting measurements to account forthe movement of the retroreflector. The position sensor within theposition detector may be any type of device capable of measuring aposition. For example, the position sensor might be a position sensitivedetector or a photosensitive array. The position sensitive detectormight be lateral effect detector or a quadrant detector, for example.The photosensitive array might be a CMOS or CCD array, for example.

In an embodiment, the return light that does not reflect off beamsplitter 145 passes through beam expander 140, thereby becoming smaller.In another embodiment, the positions of the position detector and thedistance meter are reversed so that the light reflected by the beamsplitter 145 travels to the distance meter and the light transmitted bythe beam splitter travels to the position detector.

The light continues through optional IFM, through the isolator and intothe visible light source 110. At this stage, the optical power should besmall enough so that it does not destabilize the visible light source110.

In an embodiment, the light from visible light source 110 is launchedthrough a beam launch 170 of FIG. 5. The fiber launch may be attached tothe output of light source 110 or a fiber optic output of the isolator115.

In an embodiment, the fiber network 166 of FIG. 3 is prior art fibernetwork 420B of FIG. 8B. Here the optical fibers 184, 186, 168, 169 ofFIG. 3 correspond to optical fibers 443, 444, 424, 422 of FIG. 8B. Thefiber network of FIG. 8B is like the fiber network of FIG. 8A exceptthat the fiber network of FIG. 8B has a single fiber coupler instead oftwo fiber couplers. The advantage of FIG. 8B over FIG. 8A is simplicity;however, FIG. 8B is more likely to have unwanted optical backreflections entering the optical fibers 422 and 424.

In an embodiment, the fiber network 166 of FIG. 3 is fiber network 420Cof FIG. 8C. Here the optical fibers 184, 186, 168, 169 of FIG. 3correspond to optical fibers 447, 455, 423, 424 of FIG. 8C. The fibernetwork 420C includes a first fiber coupler 445 and a second fibercoupler 451. The first fiber coupler 445 is a 2×2 coupler having twoinput ports and two output ports. Couplers of this type are usually madeby placing two fiber cores in close proximity and then drawing thefibers while heated. In this way, evanescent coupling between the fiberscan split off a desired fraction of the light to the adjacent fiber. Thesecond fiber coupler 451 is of the type called a circulator. It hasthree ports, each having the capability of transmitting or receivinglight, but only in the designated direction. For example, the light onoptical fiber 448 enters port 453 and is transported toward port 454 asindicated by the arrow. At port 454, light may be transmitted to opticalfiber 455. Similarly, light traveling on port 455 may enter port 454 andtravel in the direction of the arrow to port 456, where some light maybe transmitted to the optical fiber 424. If only three ports are needed,then the circulator 451 may suffer less losses of optical power than the2×2 coupler. On the other hand, a circulator 451 may be more expensivethan a 2×2 coupler, and it may experience polarization mode dispersion,which can be problematic in some situations.

FIGS. 9 and 10 show exploded and cross sectional views, respectively, ofa prior art laser tracker 2100, which is depicted in FIGS. 2 and 3 ofU.S. Published Patent Application No. 2010/0128259 to Bridges et al.,incorporated by reference. Azimuth assembly 2110 includes post housing2112, azimuth encoder assembly 2120, lower and upper azimuth bearings2114A, 2114B, azimuth motor assembly 2125, azimuth slip ring assembly2130, and azimuth circuit boards 2135.

The purpose of azimuth encoder assembly 2120 is to accurately measurethe angle of rotation of yoke 2142 with respect to the post housing2112. Azimuth encoder assembly 2120 includes encoder disk 2121 andread-head assembly 2122. Encoder disk 2121 is attached to the shaft ofyoke housing 2142, and read head assembly 2122 is attached to postassembly 2110. Read head assembly 2122 comprises a circuit board ontowhich one or more read heads are fastened. Laser light sent from readheads reflect off fine grating lines on encoder disk 2121. Reflectedlight picked up by detectors on encoder read head(s) is processed tofind the angle of the rotating encoder disk in relation to the fixedread heads.

Azimuth motor assembly 2125 includes azimuth motor rotor 2126 andazimuth motor stator 2127. Azimuth motor rotor comprises permanentmagnets attached directly to the shaft of yoke housing 2142. Azimuthmotor stator 2127 comprises field windings that generate a prescribedmagnetic field. This magnetic field interacts with the magnets ofazimuth motor rotor 2126 to produce the desired rotary motion. Azimuthmotor stator 2127 is attached to post frame 2112.

Azimuth circuit boards 2135 represent one or more circuit boards thatprovide electrical functions required by azimuth components such as theencoder and motor. Azimuth slip ring assembly 2130 includes outer part2131 and inner part 2132. In an embodiment, wire bundle 2138 emergesfrom auxiliary unit processor 50. Wire bundle 2138 may carry power tothe tracker or signals to and from the tracker. Some of the wires ofwire bundle 2138 may be directed to connectors on circuit boards. In theexample shown in FIG. 10, wires are routed to azimuth circuit board2135, encoder read head assembly 2122, and azimuth motor assembly 2125.Other wires are routed to inner part 2132 of slip ring assembly 2130.Inner part 2132 is attached to post assembly 2110 and consequentlyremains stationary. Outer part 2131 is attached to yoke assembly 2140and consequently rotates with respect to inner part 2132. Slip ringassembly 2130 is designed to permit low impedance electrical contact asouter part 2131 rotates with respect to the inner part 2132.

Zenith assembly 2140 comprises yoke housing 2142, zenith encoderassembly 2150, left and right zenith bearings 2144A, 2144B, zenith motorassembly 2155, zenith slip ring assembly 2160, and zenith circuit board2165.

The purpose of zenith encoder assembly 2150 is to accurately measure theangle of rotation of payload frame 2172 with respect to yoke housing2142. Zenith encoder assembly 2150 comprises zenith encoder disk 2151and zenith read-head assembly 2152. Encoder disk 2151 is attached topayload housing 2142, and read head assembly 2152 is attached to yokehousing 2142. Zenith read head assembly 2152 comprises a circuit boardonto which one or more read heads are fastened. Laser light sent fromread heads reflect off fine grating lines on encoder disk 2151.Reflected light picked up by detectors on encoder read head(s) isprocessed to find the angle of the rotating encoder disk in relation tothe fixed read heads.

Zenith motor assembly 2155 comprises azimuth motor rotor 2156 andazimuth motor stator 2157. Zenith motor rotor 2156 comprises permanentmagnets attached directly to the shaft of payload frame 2172. Zenithmotor stator 2157 comprises field windings that generate a prescribedmagnetic field. This magnetic field interacts with the rotor magnets toproduce the desired rotary motion. Zenith motor stator 2157 is attachedto yoke frame 2142.

Zenith circuit board 2165 represents one or more circuit boards thatprovide electrical functions required by zenith components such as theencoder and motor. Zenith slip ring assembly 2160 comprises outer part2161 and inner part 2162. Wire bundle 2168 emerges from azimuth outerslip ring 2131 and may carry power or signals. Some of the wires of wirebundle 2168 may be directed to connectors on circuit board. In theexample shown in FIG. 10, wires are routed to zenith circuit board 2165,zenith motor assembly 2150, and encoder read head assembly 2152. Otherwires are routed to inner part 2162 of slip ring assembly 2160. Innerpart 2162 is attached to yoke frame 2142 and consequently rotates inazimuth angle only, but not in zenith angle. Outer part 2161 is attachedto payload frame 2172 and consequently rotates in both zenith andazimuth angles. Slip ring assembly 2160 is designed to permit lowimpedance electrical contact as outer part 2161 rotates with respect tothe inner part 2162. Payload assembly 2170 includes a main opticsassembly 2180 and a secondary optics assembly 2190.

FIG. 11 is a block diagram depicting a dimensional measurementelectronics processing system 1500 that includes a laser trackerelectronics processing system 1510, processing systems of peripheralelements 1582, 1584, 1586, computer 1590, and other networked components1600, represented here as a cloud. Exemplary laser tracker electronicsprocessing system 1510 includes a master processor 1520, payloadfunctions electronics 1530, azimuth encoder electronics 1540, zenithencoder electronics 1550, display and user interface (UI) electronics1560, removable storage hardware 1565, radio frequency identification(RFID) electronics, and an antenna 1572. The payload functionselectronics 1530 includes a number of subfunctions including the six-DOFelectronics 1531, the camera electronics 1532, the ADM electronics 1533,the position detector (PSD) electronics 1534, and the level electronics1535. Most of the subfunctions have at least one processor unit, whichmight be a digital signal processor (DSP) or field programmable gatearray (FPGA), for example. The electronics units 1530, 1540, and 1550are separated as shown because of their location within the lasertracker. In an embodiment, the payload functions 1530 are located in thepayload 2170 of FIGS. 9, 10, while the azimuth encoder electronics 1540is located in the azimuth assembly 2110 and the zenith encoderelectronics 1550 is located in the zenith assembly 2140.

Many types of peripheral devices are possible, but here three suchdevices are shown: a temperature sensor 1582, a six-DOF probe 1584, anda personal digital assistant, 1586, which might be a smart phone, forexample. The laser tracker may communicate with peripheral devices in avariety of means, including wireless communication over the antenna1572, by means of a vision system such as a camera, and by means ofdistance and angular readings of the laser tracker to a cooperativetarget such as the six-DOF probe 1584. Peripheral devices may containprocessors. The six-DOF accessories may include six-DOF probing systems,six-DOF scanners, six-DOF projectors, six-DOF sensors, and six-DOFindicators. The processors in these six-DOF devices may be used inconjunction with processing devices in the laser tracker as well as anexternal computer and cloud processing resources. Generally, when theterm laser tracker processor or measurement device processor is used, itis meant to include possible external computer and cloud support.

In an embodiment, a separate communications bus goes from the masterprocessor 1520 to each of the electronics units 1530, 1540, 1550, 1560,1565, and 1570. Each communications line may have, for example, threeserial lines that include the data line, clock line, and frame line. Theframe line indicates whether or not the electronics unit should payattention to the clock line. If it indicates that attention should begiven, the electronics unit reads the current value of the data line ateach clock signal. The clock-signal may correspond, for example, to arising edge of a clock pulse. In an embodiment, information istransmitted over the data line in the form of a packet. In anembodiment, each packet includes an address, a numeric value, a datamessage, and a checksum. The address indicates where, within theelectronics unit, the data message is to be directed. The location may,for example, correspond to a processor subroutine within the electronicsunit. The numeric value indicates the length of the data message. Thedata message contains data or instructions for the electronics unit tocarry out. The checksum is a numeric value that is used to minimize thechance that errors are transmitted over the communications line.

In an embodiment, the master processor 1520 sends packets of informationover bus 1610 to payload functions electronics 1530, over bus 1611 toazimuth encoder electronics 1540, over bus 1612 to zenith encoderelectronics 1550, over bus 1613 to display and UI electronics 1560, overbus 1614 to removable storage hardware 1565, and over bus 1616 to RFIDand wireless electronics 1570.

In an embodiment, master processor 1520 also sends a synch(synchronization) pulse over the synch bus 1630 to each of theelectronics units at the same time. The synch pulse provides a way ofsynchronizing values collected by the measurement functions of the lasertracker. For example, the azimuth encoder electronics 1540 and thezenith electronics 1550 latch their encoder values as soon as the synchpulse is received. Similarly, the payload functions electronics 1530latch the data collected by the electronics contained within thepayload. The six-DOF, ADM, and position detector all latch data when thesynch pulse is given. In most cases, the camera and inclinometer collectdata at a slower rate than the synch pulse rate but may latch data atmultiples of the synch pulse period.

The azimuth encoder electronics 1540 and zenith encoder electronics 1550are separated from one another and from the payload electronics 1530 bythe slip rings 2130, 2160 shown in FIGS. 9, 10. This is why the buslines 1610, 1611, and 1612 are depicted as separate bus line in FIG. 11.

The laser tracker electronics processing system 1510 may communicatewith an external computer 1590, or it may provide computation, display,and UI functions within the laser tracker. The laser trackercommunicates with computer 1590 over communications link 1606, whichmight be, for example, an Ethernet line or a wireless connection. Thelaser tracker may also communicate with other elements 1600, representedby the cloud, over communications link 1602, which might include one ormore electrical cables, such as Ethernet cables, and one or morewireless connections. An example of an element 1600 is another threedimensional test instrument—for example, an articulated arm CMM, whichmay be relocated by the laser tracker. A communication link 1604 betweenthe computer 1590 and the elements 1600 may be wired (e.g., Ethernet) orwireless. An operator sitting on a remote computer 1590 may make aconnection to the Internet, represented by the cloud 1600, over anEthernet or wireless line, which in turn connects to the masterprocessor 1520 over an Ethernet or wireless line. In this way, a usermay control the action of a remote laser tracker.

Laser trackers today use one visible wavelength (usually red) and oneinfrared wavelength for the ADM. The red wavelength may be provided by afrequency stabilized helium-neon (HeNe) laser suitable for use in aninterferometer and also for use in providing a red pointer beam.Alternatively, the red wavelength may be provided by a diode laser thatserves just as a pointer beam. A disadvantage in using two light sourcesis the extra space and added cost required for the extra light sources,beam splitters, isolators, and other components. Another disadvantage inusing two light sources is that it is difficult to perfectly align thetwo light beams along the entire paths the beams travel. This may resultin a variety of problems including inability to simultaneously obtaingood performance from different subsystems that operate at differentwavelengths. A system that uses a single light source, therebyeliminating these disadvantages, is shown in opto-electronic system 500of FIG. 12A.

FIG. 12A includes a visible light source 110, an isolator 115, a fibernetwork 420, ADM electronics 530, a fiber launch 170, a beam splitter145, and a position detector 150. The visible light source 110 might be,for example, a red or green diode laser or a vertical cavity surfaceemitting laser (VCSEL). The isolator might be a Faraday isolator, anattenuator, or any other device capable of sufficiently reducing theamount of light fed back into the light source. The light from theisolator 115 travels into the fiber network 420, which in an embodimentis the fiber network 420A of FIG. 8A.

FIG. 12B shows an embodiment of an optoelectronic system 400 in which asingle wavelength of light is used but wherein modulation is achieved bymeans of electro-optic modulation of the light rather than by directmodulation of a light source. The optoelectronic system 400 includes avisible light source 110, an isolator 115, an electrooptic modulator410, ADM electronics 475, a fiber network 420, a fiber launch 170, abeam splitter 145, and a position detector 150. The visible light source110 may be, for example, a red or green laser diode. Laser light is sentthrough an isolator 115, which may be a Faraday isolator or anattenuator, for example. The isolator 115 may be fiber coupled at itsinput and output ports. The isolator 115 sends the light to theelectrooptic modulator 410, which modulates the light to a selectedfrequency, which may be up to 10 GHz or higher if desired. An electricalsignal 476 from ADM electronics 475 drives the modulation in theelectrooptic modulator 410. The modulated light from the electroopticmodulator 410 travels to the fiber network 420, which might be the fibernetwork 420A, 420B, 420C, or 420D discussed hereinabove. Some of thelight travels over optical fiber 422 to the reference channel of the ADMelectronics 475. Another portion of the light travels out of thetracker, reflects off retroreflector 90, returns to the tracker, andarrives at the beam splitter 145. A small amount of the light reflectsoff the beam splitter and travels to position detector 150, which hasbeen discussed hereinabove with reference to FIGS. 6A-F. A portion ofthe light passes through the beam splitter 145 into the fiber launch170, through the fiber network 420 into the optical fiber 424, and intothe measure channel of the ADM electronics 475. In general, the system500 of FIG. 12A can be manufactured for less money than system 400 ofFIG. 12B; however, the electro-optic modulator 410 may be able toachieve a higher modulation frequency, which can be advantageous in somesituations.

FIG. 13 shows an embodiment of a locator camera system 950 and anoptoelectronic system 900 in which an orientation camera 910 is combinedwith the optoelectronic functionality of a 3D laser tracker to measuresix degrees of freedom. The optoelectronic system 900 includes a visiblelight source 905, an isolator 910, an optional electrooptic modulator410, ADM electronics 715, a fiber network 420, a fiber launch 170, abeam splitter 145, a position detector 150, a beam splitter 922, and anorientation camera 910. The light from the visible light source isemitted in optical fiber 980 and travels through isolator 910, which mayhave optical fibers coupled on the input and output ports. The light maytravel through the electrooptic modulator 410 modulated by an electricalsignal 716 from the ADM electronics 715. Alternatively, the ADMelectronics 715 may send an electrical signal over cable 717 to modulatethe visible light source 905. Some of the light entering the fibernetwork travels through the fiber length equalizer 423 and the opticalfiber 422 to enter the reference channel of the ADM electronics 715. Anelectrical signal 469 may optionally be applied to the fiber network 420to provide a switching signal to a fiber optic switch within the fibernetwork 420. A part of the light travels from the fiber network to thefiber launch 170, which sends the light on the optical fiber into freespace as light beam 982. A small amount of the light reflects off thebeamsplitter 145 and is lost. A portion of the light passes through thebeam splitter 145, through the beam splitter 922, and travels out of thetracker to six degree-of-freedom (DOF) device 4000. The six-DOF device4000 may be a probe, a scanner, a projector, a sensor, or other device.

On its return path, the light from the six-DOF device 4000 enters theoptoelectronic system 900 and arrives at beamsplitter 922. Part of thelight is reflected off the beamsplitter 922 and enters the orientationcamera 910. The orientation camera 910 records the positions of somemarks placed on the retroreflector target. From these marks, theorientation angle (i.e., three degrees of freedom) of the six-DOF probeis found. The principles of the orientation camera are describedhereinafter in the present application and also in patent '758. Aportion of the light at beam splitter 145 travels through thebeamsplitter and is put onto an optical fiber by the fiber launch 170.The light travels to fiber network 420. Part of this light travels tooptical fiber 424, from which it enters the measure channel of the ADMelectronics 715.

The locator camera system 950 includes a camera 960 and one or morelight sources 970. The locator camera system is also shown in FIG. 1,where the cameras are elements 52 and the light sources are elements 54.The camera includes a lens system 962, a photosensitive array 964, and abody 966. One use of the locator camera system 950 is to locateretroreflector targets in the work volume. It does this by flashing thelight source 970, which the camera picks up as a bright spot on thephotosensitive array 964. A second use of the locator camera system 950is establish a coarse orientation of the six-DOF device 4000 based onthe observed location of a reflector spot or LED on the six-DOF device4000. If two or more locator camera systems are available on the lasertracker, the direction to each retroreflector target in the work volumemay be calculated using the principles of triangulation. If a singlelocator camera is located to pick up light reflected along the opticalaxis of the laser tracker, the direction to each retroreflector targetmay be found. If a single camera is located off the optical axis of thelaser tracker, then approximate directions to the retroreflector targetsmay be immediately obtained from the image on the photosensitive array.In this case, a more accurate direction to a target may be found byrotating the mechanical axes of the laser to more than one direction andobserving the change in the spot position on the photosensitive array.

FIG. 14 shows an embodiment of a six-DOF probe 2000 used in conjunctionwith an optoelectronic system 900 and a locator camera system 950. Theoptoelectronic system 900 and the locator camera system 950 werediscussed in reference to FIG. 13. In another embodiment, theoptoelectronic system 900 is replaced by the optoelectronic systemhaving two or more wavelengths of light. The six-DOF probe 2000 includesa body 2014, a retroreflector 2010, a probe extension assembly 2050, anoptional electrical cable 2046, an optional battery 2044, an interfacecomponent 2012, an identifier element 2049, actuator buttons 2016, anantenna 2048, and an electronics circuit board 2042. The retroreflectormay be a cube corner retroreflector with a hollow core or a glass core.The retroreflector may be marked in a way that enables determination bythe orientation camera within optoelectronic system 900 of the threeorientational degrees of freedom of the six-DOF probe 2000. An exampleof such markings is a darkening of the lines of intersection between thethree planar reflector surfaces of the retroreflector 2010, as discussedin patent '758. The probe extension assembly 2050 includes a probeextension 2052 and a probe tip 2054. The probe tip is brought intocontact with the object under test. Although the probe tip 2054 isseparated from the retroreflector 2010, it is possible for a six-DOFlaser tracker to determine the three dimensional coordinates of theprobe tip 2054 at a point hidden from the line of sight of the lightbeam 784 from the laser tracker. This is why a six-DOF probe issometimes referred to as a hidden-point probe.

Electric power may be provided over an optional electrical cable 2046 orby an optional battery 2044. The electric power provides power to anelectronics circuit board 2042. The electronics circuit board 2042provides power to the antenna 2048, which may communicate with the lasertracker or an external computer, and to actuator buttons 2016, whichprovide the user with a convenient way of communicating with the lasertracker or external computer. The electronics circuit board 2042 mayalso provide power to an LED, a material temperature sensor (not shown),an air temperature sensor (not shown), an inertial sensor (not shown) orinclinometer (not shown). The interface component 2012 may be, forexample, a light source (such as an LED), a small retroreflector, aregion of reflective material, or a reference mark. The interfacecomponent 2012 is used to establish the coarse orientation of theretroreflector 2010, which is needed in the calculations of the six-DOFangle. The identifier element 2049 is used to provide the laser trackerwith parameters or a serial number for the six-DOF probe. The identifierelement may be, for example, a bar code or an RF identification tag.

The laser tracker may alternatively provide the light beam 784 to aretroreflector 2011. By providing the light beam 784 to any of aplurality of retroreflectors, the six-DOF probe 2000 may be oriented ina wide variety of directions while probing with the probing extensionassembly 2050.

The six degrees of freedom measured by the laser tracker may beconsidered to include three translational degrees of freedom and threeorientational degrees of freedom. The three translational degrees offreedom may include a radial distance measurement, a first angularmeasurement, and a second angular measurement. The radial distancemeasurement may be made with an IFM or an ADM. The first angularmeasurement may be made with an azimuth angular measurement device, suchas an azimuth angular encoder, and the second angular measurement madewith a zenith angular measurement device. Alternatively, the firstangular measurement device may be the zenith angular measurement deviceand the second angular measurement device may be the azimuth angularmeasurement device. The radial distance, first angular measurement, andsecond angular measurement constitute three coordinates in a sphericalcoordinate system, which can be transformed into three coordinates in aCartesian coordinate system or another coordinate system.

The three orientational degrees of freedom may be determined using apatterned cube corner, as described hereinabove and in patent '758.Alternatively, other methods of determining three orientational degreesof freedom may be used. The three translational degrees of freedom andthe three orientational degrees of freedom fully define the position andorientation of the six-DOF probe 2000 in space. It is important to notethat this is the case for the systems considered here because it ispossible to have systems in which the six degrees of freedom are notindependent so that six degrees of freedom are not sufficient to fullydefine the position of a position and orientation in space. The term“translational set” is a shorthand notation for three degrees oftranslational freedom of a six-DOF accessory (such as a six-DOF probe)in the tracker frame-of-reference (or device frame of reference). Theterm “orientational set” is a shorthand notation for three orientationaldegrees of freedom of a six-DOF accessory in a tracker frame ofreference. The term “surface set” is a shorthand notation forthree-dimensional coordinates of a point on the object surface in adevice frame of reference.

FIG. 15 shows an embodiment of a six-DOF scanner 2500 used inconjunction with an optoelectronic system 900 and a locator camerasystem 950. The six-DOF scanner 2500 may also be referred to as a“target scanner.” The optoelectronic system 900 and the locator camerasystem 950 were discussed in reference to FIG. 13. In anotherembodiment, the optoelectronic system 900 is replaced by theoptoelectronic system that uses two or more wavelengths of light. Thesix-DOF scanner 2500 includes a body 2514, one or more retroreflectors2510, 2511 a scanner camera 2530, a scanner light projector 2520, anoptional electrical cable 2546, an optional battery 2444, an interfacecomponent 2512, an identifier element 2549, actuator buttons 2516, anantenna 2548, and an electronics circuit board 2542. The retroreflector2510, the optional electrical cable 2546, the optional battery 2544, theinterface component 2512, the identifier element 2549, the actuatorbuttons 2516, the antenna 2548, and the electronics circuit board 2542in FIG. 15 correspond to the retroreflector 2010, the optionalelectrical cable 2046, the optional battery 2044, the interfacecomponent 2012, the identifier element 2049, actuator buttons 2016, theantenna 2048, and the electronics circuit board 2042, respectively, inFIG. 14. The descriptions for these corresponding elements are the sameas discussed in reference to FIG. 14. Together, the scanner projector2520 and the scanner camera 2530 are used to measure the threedimensional coordinates of a workpiece 2528. The camera 2530 includes acamera lens system 2532 and a photosensitive array 2534. Thephotosensitive array 2534 may be a CCD or CMOS array, for example. Thescanner projector 2520 includes a projector lens system 2523 and asource pattern of light 2524. The source pattern of light may emit apoint of light, a line of light, or a structured (two dimensional)pattern of light. If the scanner light source emits a point of light,the point may be scanned, for example, with a moving mirror, to producea line or an array of lines. If the scanner light source emits a line oflight, the line may be scanned, for example, with a moving mirror, toproduce an array of lines. In an embodiment, the source pattern of lightmight be an LED, laser, or other light source reflected off a digitalmicromirror device (DMD) such as a digital light projector (DLP) fromTexas Instruments, an liquid crystal device (LCD) or liquid crystal onsilicon (LCOS) device, or it may be a similar device used intransmission mode rather than reflection mode. The source pattern oflight might also be a slide pattern, for example, a chrome-on-glassslide, which might have a single pattern or multiple patterns, theslides moved in and out of position as needed. Additionalretroreflectors, such as retroreflector 2511, may be added to the firstretroreflector 2510 to enable the laser tracker to track the six-DOFscanner from a variety of directions, thereby giving greater flexibilityin the directions to which light may be projected by the six-DOFprojector 2500.

The 6-DOF scanner 2500 may be held by hand or mounted, for example, on atripod, an instrument stand, a motorized carriage, or a robot endeffector. The three dimensional coordinates of the workpiece 2528 ismeasured by the scanner camera 2530 by using the principles oftriangulation. There are several ways that the triangulation measurementmay be implemented, depending on the pattern of light emitted by thescanner light source 2520 and the type of photosensitive array 2534. Forexample, if the pattern of light emitted by the scanner light source2520 is a line of light or a point of light scanned into the shape of aline and if the photosensitive array 2534 is a two dimensional array,then one dimension of the two dimensional array 2534 corresponds to adirection of a point 2526 on the surface of the workpiece 2528. Theother dimension of the two dimensional array 2534 corresponds to thedistance of the point 2526 from the scanner light source 2520. Hence thethree dimensional coordinates of each point 2526 along the line of lightemitted by scanner light source 2520 is known relative to the localframe of reference of the 6-DOF scanner 2500. The six degrees of freedomof the 6-DOF scanner are known by the six-DOF laser tracker using themethods described in patent '758. From the six degrees of freedom, thethree dimensional coordinates of the scanned line of light may be foundin the tracker frame of reference, which in turn may be converted intothe frame of reference of the workpiece 2528 through the measurement bythe laser tracker of three points on the workpiece, for example.

If the 6-DOF scanner 2500 is held by hand, a line of laser light emittedby the scanner light source 2520 may be moved in such a way as to“paint” the surface of the workpiece 2528, thereby obtaining the threedimensional coordinates for the entire surface. It is also possible to“paint” the surface of a workpiece using a scanner light source 2520that emits a structured pattern of light. Alternatively, when using ascanner 2500 that emits a structured pattern of light, more accuratemeasurements may be made by mounting the 6-DOF scanner on a tripod orinstrument stand. The structured light pattern emitted by the scannerlight source 2520 might, for example, include a pattern of fringes, eachfringe having an irradiance that varies sinusoidally over the surface ofthe workpiece 2528. In an embodiment, the sinusoids are shifted by threeor more phase values. The amplitude level recorded by each pixel of thecamera 2530 for each of the three or more phase values is used toprovide the position of each pixel on the sinusoid. This information isused to help determine the three dimensional coordinates of each point2526. In another embodiment, the structured light may be in the form ofa coded pattern that may be evaluated to determine three-dimensionalcoordinates based on single, rather than multiple, image framescollected by the camera 2530. Use of a coded pattern may enablerelatively accurate measurements while the 6-DOF scanner 2500 is movedby hand at a reasonable speed.

Projecting a structured light pattern, as opposed to a line of light,has some advantages. In a line of light projected from a handheldsix-DOF scanner 2500, the density of points may be high along the linebut much less between the lines. With a structured light pattern, thespacing of points is usually about the same in each of the twoorthogonal directions. In addition, in some modes of operation, thethree-dimensional points calculated with a structured light pattern maybe more accurate than other methods. For example, by fixing the six-DOFscanner 2500 in place, for example, by attaching it to a stationarystand or mount, a sequence of structured light patterns may be emittedthat enable a more accurate calculation than would be possible othermethods in which a single pattern was captured (i.e., a single-shotmethod). An example of a sequence of structured light patterns is one inwhich a pattern having a first spatial frequency is projected onto theobject. In an embodiment, the projected pattern is pattern of stripesthat vary sinusoidally in optical power. In an embodiment, the phase ofthe sinusoidally varying pattern is shifted, thereby causing the stripesto shift to the side. For example, the pattern may be made to beprojected with three phase angles, each shifted by 120 degrees relativeto the previous pattern. This sequence of projections provides enoughinformation to enable relatively accurate determination of the phase ofeach point of the pattern, independent of the background light. This canbe done on a point by point basis without considering adjacent points onthe object surface.

Although the procedure above determines a phase for each point withphases running from 0 to 360 degrees between two adjacent lines, theremay still be a question about which line is which. A way to identify thelines is to repeat the sequence of phases, as described above, but usinga sinusoidal pattern with a different spatial frequency (i.e., adifferent fringe pitch). In some cases, the same approach needs to berepeated for three or four different fringe pitches. The method ofremoving ambiguity using this method is well known in the art and is notdiscussed further here.

To obtain the best possible accuracy using a sequential projectionmethod such as the sinusoidal phase-shift method described above, it maybe advantageous to minimize the movement of the six-DOF scanner.Although the position and orientation of the six-DOF scanner are knownfrom the six-DOF measurements made by the laser tracker and althoughcorrections can be made for movements of a handheld six-DOF scanner, theresulting noise will be somewhat higher than it would have been if thescanner were kept stationary by placing it on a stationary mount, stand,or fixture.

The scanning methods represented by FIG. 15 are based on the principleof triangulation. A more complete explanation of the principles oftriangulation are given with reference to the system 2560 of FIG. 15Aand the system 4760 of FIG. 15B. Referring first to FIG. 15A, the system2560 includes a projector 2562 and a camera 2564. The projector 2562includes a source pattern of light 2570 lying on a source plane and aprojector lens 2572. The projector lens may include several lenselements. The projector lens has a lens perspective center 2575 and aprojector optical axis 2576. The ray of light 2573 travels from a point2571 on the source pattern of light through the lens perspective centeronto the object 2590, which it intercepts at a point 2574.

The camera 2564 includes a camera lens 2582 and a photosensitive array2580. The camera lens 2582 has a lens perspective center 2585 and anoptical axis 2586. A ray of light 2583 travels from the object point2574 through the camera perspective center 2585 and intercepts thephotosensitive array 2580 at point 2581.

The line segment that connects the perspective centers is the baseline2588 in FIG. 15A and the baseline 4788 in FIG. 15B. The length of thebaseline is called the baseline length (2592, 4792). The angle betweenthe projector optical axis and the baseline is the baseline projectorangle (2594, 4794). The angle between the camera optical axis (2583,4786) and the baseline is the baseline camera angle (2596, 4796). If apoint on the source pattern of light (2570, 4771) is known to correspondto a point on the photosensitive array (2581, 4781), then it is possibleusing the baseline length, baseline projector angle, and baseline cameraangle to determine the sides of the triangle connecting the points 2585,2574, and 2575, and hence determine the surface coordinates of points onthe surface of object 2590 relative to the frame of reference of themeasurement system 2560. To do this, the angles of the sides of thesmall triangle between the projector lens 2572 and the source pattern oflight 2570 are found using the known distance between the lens 2572 andplane 2570 and the distance between the point 2571 and the intersectionof the optical axis 2576 with the plane 2570. These small angles areadded or subtracted from the larger angles 2596 and 2594 as appropriateto obtain the desired angles of the triangle. It will be clear to one ofordinary skill in the art that equivalent mathematical methods can beused to find the lengths of the sides of the triangle 2574-2585-2575 orthat other related triangles may be used to obtain the desiredcoordinates of the surface of object 2590.

Referring first to FIG. 15B, the system 4760 is similar to the system2560 of FIG. 15A except that the system 4760 does not include a lens.The system may include a projector 4762 and a camera 4764. In theembodiment illustrated in FIG. 15B, the projector includes a lightsource 4778 and a light modulator 4770. The light source 4778 may be alaser light source since such a light source may remain in focus for along distance using the geometry of FIG. 15B. A ray of light 4773 fromthe light source 4778 strikes the optical modulator 4770 at a point4771. Other rays of light from the light source 4778 strike the opticalmodulator at other positions on the modulator surface. In an embodiment,the optical modulator 4770 changes the power of the emitted light, inmost cases by decreasing the optical power to a degree. In this way, theoptical modulator imparts an optical pattern to the light, referred tohere as the source pattern of light, which is at the surface of theoptical modulator 4770. The optical modulator 4770 may be a DLP or LCOSdevice for example. In some embodiments, the modulator 4770 istransmissive rather than reflective. The light emerging from the opticalmodulator 4770 appears to emerge from a virtual light perspective center4775. The ray of light appears to emerge from the virtual lightperspective center 4775, pass through the point 4771, and travel to thepoint 4774 at the surface of object 4790.

The baseline is the line segment extending from the camera lensperspective center 4785 to the virtual light perspective center 4775. Ingeneral, the method of triangulation involves finding the lengths of thesides of a triangle, for example, the triangle having the vertex points4774, 4785, and 4775. A way to do this is to find the length of thebaseline, the angle between the baseline and the camera optical axis4786, and the angle between the baseline and the projector referenceaxis 4776. To find the desired angle, additional smaller angles arefound. For example, the small angle between the camera optical axis 4786and the ray 4783 can be found by solving for the angle of the smalltriangle between the camera lens 4782 and the photosensitive array 4780based on the distance from the lens to the photosensitive array and thedistance of the pixel from the camera optical axis. The angle of thesmall triangle is then added to the angle between the baseline and thecamera optical axis to find the desired angle. Similarly for theprojector, the angle between the projector reference axis 4776 and theray 4773 is found can be found by solving for the angle of the smalltriangle between these two lines based on the known distance of thelight source 4777 and the surface of the optical modulation and thedistance of the projector pixel at 4771 from the intersection of thereference axis 4776 with the surface of the optical modulator 4770. Thisangle is subtracted from the angle between the baseline and theprojector reference axis to get the desired angle.

The camera 4764 includes a camera lens 4782 and a photosensitive array4780. The camera lens 4782 has a camera lens perspective center 4785 anda camera optical axis 4786. The camera optical axis is an example of acamera reference axis. From a mathematical point of view, any axis thatpasses through the camera lens perspective center may equally easily beused in the triangulation calculations, but the camera optical axis,which is an axis of symmetry for the lens, is customarily selected. Aray of light 4783 travels from the object point 4774 through the cameraperspective center 4785 and intercepts the photosensitive array 4780 atpoint 4781. Other equivalent mathematical methods may be used to solvefor the lengths of the sides of a triangle 4774-4785-4775, as will beclear to one of ordinary skill in the art.

Although the triangulation method described here is well known, someadditional technical information is given hereinbelow for completeness.Each lens system has an entrance pupil and an exit pupil. The entrancepupil is the point from which the light appears to emerge, whenconsidered from the point of view of first-order optics. The exit pupilis the point from which light appears to emerge in traveling from thelens system to the photosensitive array. For a multi-element lenssystem, the entrance pupil and exit pupil do not necessarily coincide,and the angles of rays with respect to the entrance pupil and exit pupilare not necessarily the same. However, the model can be simplified byconsidering the perspective center to be the entrance pupil of the lensand then adjusting the distance from the lens to the source or imageplane so that rays continue to travel along straight lines to interceptthe source or image plane. In this way, the simple and widely used modelshown in FIG. 15A is obtained. It should be understood that thisdescription provides a good first order approximation of the behavior ofthe light but that additional fine corrections can be made to accountfor lens aberrations that can cause the rays to be slightly displacedrelative to positions calculated using the model of FIG. 15A. Althoughthe baseline length, the baseline projector angle, and the baselinecamera angle are generally used, it should be understood that sayingthat these quantities are required does not exclude the possibility thatother similar but slightly different formulations may be applied withoutloss of generality in the description given herein.

When using a six-DOF scanner, several types of scan patterns may beused, and it may be advantageous to combine different types to obtainthe best performance in the least time. For example, in an embodiment, afast measurement method uses a two-dimensional coded pattern in whichthree-dimensional coordinate data may be obtained in a single shot. In amethod using coded patterns, different characters, different shapes,different thicknesses or sizes, or different colors, for example, may beused to provide distinctive elements, also known as coded elements orcoded features. Such features may be used to enable the matching of thepoint 2571 to the point 2581. A coded feature on the source pattern oflight 2570 may be identified on the photosensitive array 2580.

A technique that may be used to simplify the matching of coded featuresis the use of epipolar lines. Epipolar lines are mathematical linesformed by the intersection of epipolar planes and the source plane 2570or the image plane 2580. An epipolar plane is any plane that passesthrough the projector perspective center and the camera perspectivecenter. The epipolar lines on the source plane and image plane may beparallel in some special cases, but in general are not parallel. Anaspect of epipolar lines is that a given epipolar line on the projectorplane has a corresponding epipolar line on the image plane. Hence, anyparticular pattern known on an epipolar line in the projector plane maybe immediately observed and evaluated in the image plane. For example,if a coded pattern is placed along an epipolar line in the projectorplane that the spacing between coded elements in the image plane may bedetermined using the values read out by pixels of the photosensitivearray 2580 and this information used to determine the three-dimensionalcoordinates of an object point 2574. It is also possible to tilt codedpatterns at a known angle with respect to an epipolar line andefficiently extract object surface coordinates.

An advantage of using coded patterns is that three-dimensionalcoordinates for object surface points can be quickly obtained. However,in most cases, a sequential structured light approach, such as thesinusoidal phase-shift approach discussed above, will give more accurateresults. Therefore, the user may advantageously choose to measurecertain objects or certain object areas or features using differentprojection methods according to the accuracy desired. By using aprogrammable source pattern of light, such a selection may easily bemade.

An important limitation in the accuracy of scanners may be present forcertain types of objects. For example, some features such as holes orrecesses may be difficult to scan effectively. The edges of objects orholes may be difficult to obtain as smoothly as might be desired. Sometypes of materials may not return as much light as desired or may have alarge penetration depth for the light. In other cases, light may reflectoff more than one surface (multipath interference) before returning tothe scanner so that the observed light is “corrupted,” thereby leadingto measurement errors. In any of these cases, it may be advantageous tomeasure the difficult regions using a six-DOF scanner 2505 shown in FIG.15C that includes a tactile probe such as the probe tip 2554, which ispart of the probe extension assembly 2550. After it has been determinedthat it would be advantageous to measure with a tactile probe, theprojector 2520 may send a laser beam to illuminate the region to bemeasured. In FIG. 15C, a projected ray of beam of light 2522 isilluminating a point 2527 on an object 2528, indicating that this pointis to be measured by the probe extension assembly 2550. In some cases,the tactile probe may be moved outside the field of projection of theprojector 2550 so as to avoid reducing the measurement region of thescanner. In this case, the beam 2522 from the projector may illuminate aregion that the operator may view. The operator can then move thetactile probe 2550 into position to measure the prescribed region. Inother cases, the region to be measured may be outside the projectionrange of the scanner. In this case, the scanner may point the beam 2522to the extent of its range in the direction to be measured or it maymove the beam 2522 in a pattern indicating the direction to which thebeam should be placed. Another possibility is to present a CAD model orcollected data on a display monitor and then highlight on the displaythose regions of the CAD model or collected data that should bere-measured. It is also possible to measure highlighted regions usingother tools, for example, a spherically mounted retroreflector or asix-DOF probe under control of a laser tracker.

The projector 2520 may project a two dimensional pattern of light, whichis sometimes called structured light. Such light emerges from theprojector lens perspective center and travels in an expanding patternoutward until it intersects the object 2528. Examples of this type ofpattern are the coded pattern and the periodic pattern, both discussedhereinabove. The projector 2520 may alternatively project aone-dimensional pattern of light. Such projectors are sometimes referredto as laser line probes or laser line scanners. Although the lineprojected with this type of scanner has width and a shape (for example,it may have a Gaussian beam profile in cross section), the informationit contains for the purpose of determining the shape of an object is onedimensional. So a line emitted by a laser line scanner intersects anobject in a linear projection. The illuminated shape traced on theobject is two dimensional. In contrast, a projector that projects atwo-dimensional pattern of light creates an illuminated shape on theobject that is three dimensional. One way to make the distinctionbetween the laser line scanner and the structured light scanner is todefine the structured light scanner as a type of scanner that containsat least three non-collinear pattern elements. For the case of atwo-dimensional pattern that projects a coded pattern of light, thethree non-collinear pattern elements are recognizable because of theircodes, and since they are projected in two dimensions, the at leastthree pattern elements must be non-collinear. For the case of theperiodic pattern, such as the sinusoidally repeating pattern, eachsinusoidal period represents a plurality of pattern elements. Sincethere is a multiplicity of periodic patterns in two dimensions, thepattern elements must be non-collinear. In contrast, for the case of thelaser line scanner that emits a line of light, all of the patternelements lie on a straight line. Although the line has width and thetail of the line cross section may have less optical power than the peakof the signal, these aspects of the line are not evaluated separately infinding surface coordinates of an object and therefore do not representseparate pattern elements. Although the line may contain multiplepattern elements, these pattern elements are collinear.

A method for calculating three dimensional coordinates of an objectsurface is now given with reference to FIG. 15D. The line scanner system4500 includes a projector 4520 and a camera 4540. The projector 4520includes a source pattern of light 4521 and a projector lens 4522. Thesource pattern of light includes an illuminated pattern in the form of aline. The projector lens includes a projector perspective center and aprojector optical axis that passes through the projector perspectivecenter. In the example of FIG. 15D, a central ray of the beam of light4524 is aligned with the perspective optical axis. The camera 4540includes a camera lens 4542 and a photosensitive array 4541. The lenshas a camera optical axis 4543 that passes through a camera lensperspective center 4544. In the exemplary system 4500, the projectoroptical axis, which is aligned to the beam of light 4524, and the cameralens optical axis 4544, are perpendicular to the line of light 4526projected by the source pattern of light 4521. In other words, the line4526 is in the direction perpendicular to the paper in FIG. 15D. Theline strikes an object surface, which at a first distance from theprojector is object surface 4510A and at a second distance from theprojector is object surface 4520A. It is understood that at differentheights above or below the paper of FIG. 15D, the object surface may beat a different distance from the projector than the distance to eitherobject surface 4520A or 4520B. For a point on the line of light 4526that also lies in the paper of FIG. 15D, the line of light intersectssurface 4520A in a point 4526 and it intersects the surface 4520B in apoint 4527. For the case of the intersection point 4526, a ray of lighttravels from the point 4526 through the camera lens perspective center4544 to intersect the photosensitive array 4541 in an image point 4546.For the case of the intersection point 4527, a ray of light travels fromthe point 4527 through the camera lens perspective center to intersectthe photosensitive array 4541 in an image point 4547. By noting theposition of the intersection point relative to the position of thecamera lens optical axis 4544, the distance from the projector (andcamera) to the object surface can be determined. The distance from theprojector to other points on the line of light 4526, that is points onthe line of light that do not lie in the plane of the paper of FIG. 15D,may similarly be found. In the usual case, the pattern on thephotosensitive array will be a line of light (in general, not a straightline), where each point in the line corresponds to a different positionperpendicular to the plane of the paper, and the position perpendicularto the plane of the paper contains the information about the distancefrom the projector to the camera. Therefore, by evaluating the patternof the line in the image of the photosensitive array, thethree-dimensional coordinates of the object surface along the projectedline can be found. Note that the information contained in the image onthe photosensitive array for the case of a line scanner is contained ina (not generally straight) line. In contrast, the information containedin the two-dimensional projection pattern of structured light containsinformation over both dimensions of the image in the photosensitivearray.

It should be noted that although the descriptions given abovedistinguish between line scanners and area (structured light) scannersbased on whether three or more pattern elements are collinear, it shouldbe noted that the intent of this criterion is to distinguish patternsprojected as areas and as lines. Consequently patterns projected in alinear fashion having information only along a single path are stillline patterns even though the one-dimensional pattern may be curved.

An important advantage that a line scanner may have over a structuredlight scanner in some cases is in its greater ability to detect themultipath interference. In an ordinary (desired) case, each ray of lightemerging from the projector and striking the object surface may beconsidered to generally reflect in a direction away from the object. Forthe usual case, the surface of the object is not highly reflective(i.e., a mirror like surface), so that almost all of the light isdiffusely reflected (scattered) rather than being specularly reflected.The diffusely reflected light does not all travel in a single directionas would reflected light in the case of a mirror-like surface but ratherscatters in a pattern. The general direction of the scattered light maybe found in the same fashion as in the reflection of light off amirror-like surface, however. This direction may be found by drawing anormal to the surface of the object at the point of intersection of thelight from the projector with the object. The general direction of thescattered light is then found as the reflection of the incident lightabout the surface normal. In other words, the angle of reflection isequal to the angle of incidence, even though the angle of reflection isonly a general scattering direction in this case.

The case of multipath interference occurs when the some of the lightthat strikes the object surface is first scattered off another surfaceof the object before returning to the camera. For the point on theobject that receives this scattered light, the light sent to thephotosensitive array then corresponds not only to the light directlyprojected from the projector but also to the light sent to a differentpoint on the projector and scattered off the object. The result ofmultipath interference, especially for the case of scanners that projecttwo-dimensional (structured) light, may be to cause the distancecalculated from the projector to the object surface at that point to beinaccurate.

For the case of a line scanner, there is a way to determine if multipathinterference is present. In an embodiment, the rows of a photosensitivearray are parallel to the plane of the paper in FIG. 15E and the columnsare perpendicular to the plane of the paper. Each row represents onepoint on the projected line 4526 in the direction perpendicular to theplane of the paper. In an embodiment, the distance from the projector tothe object for that point on the line is found by first calculating thecentroid for each row. However, the light on each row should beconcentrated over a region of contiguous pixels. If there are two ormore regions that receive a significant amount of light, multipathinterference is indicated. An example of such a multipath interferencecondition and the resulting extra region of illumination on thephotosensitive array are shown in FIG. 15E. The surface 4510A now has agreater curvature near the point of intersection 4526. The surfacenormal at the point of intersection is the line 4528, and the angle ofincidence is 4531. The direction of the reflected line of light 4529 isfound from the angle of reflection 4532, which is equal to the angle ofincidence. As stated hereinabove, the line of light 4529 actuallyrepresents an overall direction for light that scatters over a range ofangles. The center of the scattered light strikes the object 4510A atthe point 4527, which is imaged by the lens 4544 at the point 4548 onthe photosensitive array. The unexpectedly high amount of light receivedin the vicinity of point 4548 indicates that multipath interference isprobably present. For a line scanner, the main concern with multipathinterference is not for the case shown in FIG. 15E, where the two spots4546 and 4541 are separated by a considerable distance and can beanalyzed separately but rather for the case in which the two spotsoverlap or smear together. In this case, it is not possible to determinethe centroid corresponding to the desired point, which in FIG. 15Ecorresponds to the point 4546. The problem is made worse for the case ofa scanner that projects light in two dimensions as can be understood byagain referring to FIG. 15E. If all of the light imaged onto thephotosensitive array 4541 were needed to determine two-dimensionalcoordinates, then it is clear that the light at the point 4527 wouldcorrespond to the desired pattern of light directly projected from theprojector as well as the unwanted light reflected to the point 4527 froma reflection off the object surface. As a result, in this case, thewrong three dimensional coordinates would likely be calculated for thepoint 4527 for two dimensional projected light.

For a projected line of light, in many cases, it is possible toeliminate multipath interference by changing the direction of the line.One possibility is to make a line scanner using a projector havinginherent two-dimensional capability, thereby enabling the line to beswept or to be automatically rotated to different directions. Forexample, if multipath interference were suspected in a particular scanobtained with structured light, a measurement system could beautomatically configured to switch to a measurement method using a sweptline of light.

Another more complete way to eliminate multipath interference is tosweep a point of light, rather than a line of light or an area of light,over those regions for which multipath interference has been indicated.By illuminating a single point of light, no other illuminated points canreflect scattered light onto the point intended for measurement. Forexample, if the line 4526 were scanned as a collection of individualspots of light, the chance of multipath interference would beeliminated.

Another reflection problem that can be encountered when making scannermeasurements is that of reflected specular light. Sometimes, arelatively smooth surface will have a curvature such that a large amountof light is specularly reflected onto the photosensitive array, therebycreating a “hot spot” that gets more light than surrounding pixels. Suchhot spots of light are sometimes referred to as “glints.” These hotspots can make it difficult to measure an object properly with ascanner. As in the case of multipath interference, the problem of glintsmay be overcome by using a laser line having an adjustable direction ora spot.

It is easy to determine if a glint is present since small saturatedregions on a photosensitive array can readily be detected. However, asystematic approach is needed to identify and overcome multipathproblems. A general approach may be used to evaluate not only multipathinterference but also quality in general, including resolution andeffect of material type, surface quality, and geometry. Referring alsoto FIG. 15F, in an embodiment, a method 4600 may be carried outautomatically under computer control. A step 4602 is to determinewhether information on three-dimensional coordinates of an object undertest are available. A first type of three-dimensional information is CADdata. CAD data usually indicates nominal dimensions of an object undertest. A second type of three-dimensional information is measuredthree-dimensional data—for example, data previously measured with ascanner or other device. In some cases, the step 4602 may include afurther step of aligning the frame of reference of the coordinatemeasurement device, for example, laser tracker or six-DOF scanneraccessory, with the frame of reference of the object. In an embodiment,this is done by measuring at least three points on the surface of theobject with the laser tracker.

If the answer to the question posed in step 4602 is that thethree-dimensional information is available, then, in a step 4604, thecomputer or processor is used to calculate the susceptibility of theobject measurement to multipath interference. In an embodiment, this isdone by projecting each ray of light emitted by the scanner projector,and calculating the angle or reflection for each case. An example, givenfor the line scanner case, was described with reference to FIG. 5E. Thecalculations for the structured light scanner are carried out in thesame way. The computer or software identifies each region of the objectsurface that is susceptible to error as a result of multipathinterference. The step 4604 may also carry out an analysis of thesusceptibility to multipath error for a variety of positions of thesix-DOF probe relative to the object under test. In some cases,multipath interference may be avoided or minimize by selecting asuitable position and orientation of the six-DOF probe relative to theobject under test. If the answer to the question posed in step 4602 isthat three-dimensional information is not available, then a step 4606 isto measure the three-dimensional coordinates of the object surface usingany desired or preferred measurement method. Following the calculationof multipath interference, a step 4608 may be carried out to evaluateother aspects of expected scan quality. One such quality factor iswhether the resolution of the scan is sufficient for the features of theobject under test. For example, if the resolution of a device is 3 mm,and there are sub-millimeter features for which valid scan data isdesired, then these problem regions of the object should be noted forlater corrective action. Another quality factor related partly toresolution is the ability to measure edges of the object and edges ofholes. Knowledge of scanner performance will enable a determination ofwhether the scanner resolution is good enough for given edges. Anotherquality factor is the amount of light expected to be returned from agiven feature. Little if any light may be expected to be returned to thescanner from inside a small hole, for example, or from a glancing angle.Also, little light may be expected from certain kinds and colors ofmaterials. Certain types of materials may have a large depth ofpenetration for the light from the scanner, and in this case goodmeasurement results would not be expected. In some cases, an automaticprogram may ask for user supplementary information. For example, if acomputer program is carrying out steps 4604 and 4608 based on CAD data,it may not know the type of material being used or the surfacecharacteristics of the object under test. In these cases, the step 4608may include a further step of obtaining material characteristics for theobject under test.

Following the analysis of steps 4604 and 4608, the step 4610 is todecide whether further diagnostic procedures should be carried out. Afirst example of a possible diagnostic procedure is the step 4612 ofprojecting a stripe at a preferred angle to note whether multipathinterference is observed. The general indications of multipathinterference for a projected line stripe were discussed hereinabove withreference to FIG. 15E. Another example of a diagnostic step is step4614, which is to project a collection of lines aligned in the directionof epipolar lines on the source pattern of light, for example, thesource pattern of light 2570 in FIG. 15A or the source pattern of lightat 4770 in FIG. 15B. For the case in which lines of light in the sourcepattern of light are aligned to the epipolar lines, then these lineswill also appear as straight lines in the image plane on thephotosensitive array, for example, at the plane 2580 of FIG. 15A or theplane 4780 of FIG. 15B. If these patterns on the photosensitive arrayare not straight lines or if the lines are blurred or noisy, then aproblem is indicated, possibly as a result of multipath interference.

The step 4616 is to select a combination of preferred actions based onthe analyses and diagnostic procedure performed. If speed in ameasurement is particularly important, a step 4618 of measuring using a2D (structured) pattern of coded light may be preferred. If greateraccuracy is more important, then a step 4620 of measuring using a 2D(structured) pattern of coded light using sequential patterns, forexample, a sequence of sinusoidal patterns of varying phase and pitch,may be preferred. If the method 4618 or 4620 is selected, then it may bedesirable to also select a step 4628, which is to reposition thescanner, in other words to adjust the position and orientation of thescanner to the position that minimizes multipath interference andspecular reflections (glints) as provided by the analysis of step 4604.Such indications may be provided to a user by illuminating problemregions with light from the scanner projector or by displaying suchregions on a monitor display. Alternatively, the next steps in themeasurement procedure may be automatically selected by a computer orprocessor. If the preferred scanner position does not eliminatemultipath interference and glints, several options are available. Insome cases, the measurement can be repeated with the scannerrepositioned and the valid measurement results combined. In other cases,alternative measurement steps may be added to the procedure or performedinstead of using structured light. As discussed previously, a step 4622of scanning a stripe of light provides a convenient way of obtaininginformation over an area with reduced chance of having a problem frommultipath interference. A step 4624 of sweeping a small spot of lightover a region of interest further reduces the chance of problems frommultipath interference. A step of measuring a region of an objectsurface with a tactile probe or another mechanical sensor such as an SMReliminates the possibility of multipath interference. A tactile probeprovides a known resolution based on the size of the probe tip, and iteliminates issues with low reflectance of light or large opticalpenetration depth, which might be found in some objects under test.

In most cases, the quality of the data collected in a combination of thesteps 4618-4628 may be evaluated in a step 4630 based on the dataobtained from the measurements, combined with the results of theanalyses carried out previously. If the quality is found to beacceptable in a step 4632, the measurement is completed at a step 4634.Otherwise, the analysis resumes at the step 4604. In some cases, the 3Dinformation may not have been as accurate as desired. In this case,repeating some of the earlier steps may be helpful.

In another embodiment, the camera 2530 and projector 2520 may beconfigured to measure features that are too small to be seen by thehuman eye. In general, for this application, the structured lightpatterns will be reduced in size with the camera configured to measure apattern of this size. Examples of applications using this type ofprojector 2500 include measuring of small weld spots, measuring ofsurface roughness and waviness, measuring of properties of materialssuch as paper, measuring of cutting edges, measuring of wear, abrasion,and erosion, measuring of planarity and step height. The scanner systemof FIG. 15, which includes a six-DOF scanner and a laser tracker,enables the measurement of small features over large areas.

FIG. 16 shows an embodiment of a six-DOF indicator 2800 used inconjunction with an optoelectronic system 900 and a locator camerasystem 950. The optoelectronic system 900 and the locator camera system950 were discussed in conjunction with FIG. 13, and this discussion willnot be repeated here. In an embodiment, the optoelectronic system 900 isreplaced by the optoelectronic system 1900. The six-DOF indicator 2800includes a body 2814, one or more retroreflectors 2810, 2811, a mount2890, an optional electrical cable 2836, an optional battery 2834, aninterface component 2812, an identifier element 2839, actuator buttons2816, an antenna 2838, and an electronics circuit board 2832. Theretroreflector 2810, the optional electrical cable 2836, the optionalbattery 2834, the interface component 2812, the identifier element 2839,the actuator buttons 2816, the antenna 2838, and the electronics circuitboard 2832 in FIG. 16 correspond to the retroreflector 2010, theoptional electrical cable 2046, the optional battery 2044, the interfacecomponent 2012, the identifier element 2049, actuator buttons 2016, theantenna 2048, and the electronics circuit board 2042, respectively, inFIG. 14. The descriptions for these corresponding elements are the sameas discussed hereinabove and will not be repeated. The mount 2890 may beattached to a moving element, thereby enabling the laser tracker tomeasure the six degrees of moving element. The moving element may be arobotic end effector, a machine tool, or a tool on an assembly (e.g., anassembly line carriage). The six-DOF indicator can be compact becausethe retroreflector 2810 may be small and most other elements of FIG. 16are optional and can be omitted. This small size may provide anadvantage in some cases. Additional retroreflectors, such asretroreflector 2611, may be added to the first retroreflector 2610 toenable the laser tracker to track the six-DOF scanner from a variety ofdirections.

FIG. 16A shows an embodiment in which the six-DOF indicator 4730 is asix-DOF spherically mounted retroreflector (SMR) 4734 mounted on amagnetic nest 4732. The six-DOF SMR may contain a patternedretroreflector, which might be an open air or glass retroreflectorhaving markings along the intersections of the reflecting elements. Inan embodiment, the initial orientation of the six-DOF indicator isdetermined by the operator by positioning the six-DOF SMR in a preferredorientation, for example, with a mark or a label pointed upwards. Withthis method, the six-DOF indicator can be completely passive, notrequiring any electrical powers or any electrical signals from any otherdevice. Such a six-DOF indicator provides considerable advantages sincemagnetic nests can be quickly and easily mounted at any desiredlocation—for example, on a robot or a machine tool, without requiringany electrical cables or complex fixturing to be installed. In anembodiment, the magnetic nest 4732 is attached to the device, whichmight be a robot or machine tool, with a threaded screw attached tothreaded opening 4734. In other embodiments, the magnetic nest isattached to the device with hot glue or epoxy.

FIG. 16B shows an embodiment 4760 in which the six-DOF indicator 4734 isa six-DOF SMR mounted on a nest 4732 having a constraint 4762. Theconstraint includes an element that comes in contact with the six-DOFSMR 4734—for example, a machined piece of metal, a plastic cover, or astrap. The constraint is brought into tight physical contact with thesix-DOF SMR 4734 by means of a securing mechanism 4764. Examples ofsecuring mechanisms including hooking clamps and screw clamp. Theconstraint 4762 provides protection against bumps or high accelerations.

FIG. 17 shows an embodiment of a six-DOF projector 2600 used inconjunction with an optoelectronic system 900 and a locator camerasystem 950. The optoelectronic system 900 and the locator camera system950 were discussed in conjunction with FIG. 13, and that discussion willnot be repeated here. In an embodiment, the optoelectronic system 900 isreplaced by the optoelectronic system having two or more wavelengths oflight. The six-DOF projector 2600 includes a body 2614, one or moreretroreflectors 2610, 2611, a projector 2620, an optional electricalcable 2636, an optional battery 2634, an interface component 2612, anidentifier element 2639, actuator buttons 2616, an antenna 2638, and anelectronics circuit board 2632. The retroreflector 2610, the optionalelectrical cable 2636, the optional battery 2634, the interfacecomponent 2612, the identifier element 2639, the actuator buttons 2616,the antenna 2638, and the electronics circuit board 2632 of FIG. 17correspond to the retroreflector 2010, the optional electrical cable2046, the optional battery 2044, the interface component 2012, theidentifier element 2049, actuator buttons 2016, the antenna 2048, andthe electronics circuit board 2042, respectively, in FIG. 14. Thedescriptions for these corresponding elements are the same as discussedhereinabove and will not be repeated. The six-DOF projector 2600 mayinclude a light source, a light source and a steering mirror, a MEMSmicromirror, a liquid crystal projector, or any other device capable ofprojecting a pattern of light onto a workpiece 2600. The six degrees offreedom of the projector 2600 are known by the laser tracker using themethods described in patent '758. From the six degrees of freedom, thethree dimensional coordinates of the projected pattern of light may befound in the tracker frame of reference, which in turn may be convertedinto the frame of reference of the workpiece through the measurement bythe laser tracker of three points on the workpiece, for example.Additional retroreflectors, such as retroreflector 2611, may be added tothe first retroreflector 2610 to enable the laser tracker to track thesix-DOF scanner from a variety of directions, thereby giving greaterflexibility in the directions to which light may be projected by thesix-DOF projector 2600.

With the projected pattern of light 2640 on the surface of the workpiece2660 known in the frame of reference of the workpiece, a variety ofuseful capabilities can be obtained. As a first example, the projectedpattern may indicate where an operator should drill holes or performother operations to enable the affixing of components onto the workpiece2660. For example, gauges may be attached to the cockpit of an aircraft.Such a method of in-situ assembly can be cost effective in many cases.As a second example, the projected pattern may indicate where materialneeds to be added to or removed from a tool through the use of contourpatterns, color coded tolerance patterns, or other graphical means. Anoperator may use a tool to abrade unwanted material or use a fillermaterial to fill in an area. Because the laser tracker or an externalcomputer attached to the laser tracker may know the details of the CADmodel, the six-DOF projector can provide a relatively fast and simplemethod for modifying a tool to meet CAD tolerances. Other assemblyoperations might include scribing, applying adhesive, applying acoating, applying a label, and cleaning As a third example, theprojected pattern may indicate hidden components. For example, tubing orelectrical cables may be routed behind a surface and hidden from view.The location of these components may be projected onto the workpiece,thereby enabling the operator to avoid them in performing assembly orrepair operations.

To project light from the projector scanner into the frame of referenceof the workpiece, it is generally necessary to determine the frame ofreference of the workpiece in the frame of reference of the lasertracker. One way to do this is to measure three points on the surface ofthe workpiece with the laser tracker. Then a CAD model or previouslymeasured data may be used to establish a relationship between aworkpiece and a laser tracker.

When an operator performs assembly operations with the assistance of asix-DOF projector, a useful technique is to mount the six-DOF projectoron a stationary stand or mount, thereby enabling the operator to performassembly operations with both hands free. A useful mode of the lasertracker and six-DOF projector is to have the six-DOF projector continueto project a pattern of light even after the laser tracker ceases totrack the retroreflector on the six-DOF scanner. In this way, theoperator may use the laser tracker to perform measurements, for example,with an SMR, a six-DOF probe, or a six-DOF scanner while the projectorcontinues to display the pattern of light that indicates the assemblyoperations to be performed. In a similar manner, the tracker may be usedto set up two or more scanner projectors that continue to projectpatterns after the tracker has stopped tracking the retroreflector oneach scanner projector. Hence high levels of detail may be projectedonto relatively large areas, enabling assistance to several operatorssimultaneously. It is also possible in a mode to enable the six-DOFscanner to project any of several alternative patterns, thereby enablingthe operator to perform assembly operations is a prescribed sequence.

Besides assisting with assembly operations, the projector scanner canalso assist in carrying out inspection procedures. In some cases, aninspection procedure may call for an operator to perform a sequence ofmeasurements in a particular order. The six-DOF scanner may point to thepositions at which the operator is to make a measurement at each step.The six-DOF scanner may demarcate a region over which a measurement isto be made. For example, by drawing a box, the six-DOF scanner mayindicate that the operator is to perform a scanning measurement over theregion inside the box, perhaps to determine the flatness of the regionsor maybe as part of a longer measurement sequence. Because the projectorcan continue the sequence of steps with the six-DOF retroreflector beingtracked by the laser tracker, the operator may continue an inspectionsequence using the tracker or using other tools. If the tracker isperforming the measurements, it will know when measurements have beensuccessfully completed and may move onto the next step. The projectorscanner may also provide information to the operator in the form ofwritten messages or audio messages. The operator may signal commands tothe laser tracker using gestures that may be picked up by the trackercameras or by other means.

The six-DOF projector may use patterns of light, perhaps applieddynamically, to convey information. For example, the six-DOF projectormay use a back and forth motion to indicate a direction to which an SMRis to be moved. The six-DOF projector may draw other patterns to givemessages that may be interpreted by an operator according to a set ofrules, the rules which may be available to the user in written ordisplayed form.

The six-DOF projector may also be used to convey information to the userabout the nature of an object under investigation. For example, ifdimensional measurements have been performed, the six-DOF projectormight project a color coded pattern indicating regions of errorassociated in the surface coordinates of the object under test. It may,alternatively, just display regions or values that are out of tolerance.It may, for example, highlight a region for which the surface profile isoutside the tolerance. Alternatively, it may draw a line to indicate alength measured between two points and then write a message on the partindicating the amount of error associated with that distance.

The six-DOF projector may also display information about measuredcharacteristics besides dimensional characteristics, wherein thecharacteristics are tied to coordinate positions on the object. Suchcharacteristics of an object under test may include temperature values,ultrasound values, microwave values, millimeter-wave values, X-rayvalues, radiological values, chemical sensing values, and many othertypes of values. Such object characteristics may be measured andmatching to three-dimensional coordinates on an object using a six-DOFscanner, as discussed hereinafter. Alternatively, characteristics of anobject may be measured on the object using a separate measurementdevice, with the data correlated in some way to dimensional coordinatesof the object surface with an object frame of reference. Then bymatching the frame of reference of the object to the frame of referenceof the laser tracker or the six-DOF projector, information about theobject characteristics may be displayed on the object, for example, ingraphical form. For example, temperature values of an object surface maybe measured using a thermal array. Each of the temperatures may berepresented by a color code projected onto the object surface.

A six-DOF scanner may also project modeled data onto an object surface.For example, it might project the results of a thermal finite elementanalysis (FEA) onto the object surface and then allow the operator toselect which of two displays—FEA or measured thermal data—is displayedat any one time. Because both sets of data are projected onto the objectat the actual positions where the characteristic is found—for example,the positions at which particular temperatures have been measured orpredicted to exist, the user is provided with a clear and immediateunderstanding of the physical effects affecting the object. The six-DOFprojector may also be attached to a moveable carrier such as a robot ormachine tool.

If a measurement of a small region has been made with features resolvedthat are too small for the human eye to see, the six-DOF projector mayproject a magnified view of those characteristics previously measuredover a portion of the object surface onto the object surface, therebyenabling the user to see features too small to be seen withoutmagnification. In an embodiment, the high resolution measurement is madewith a six-DOF scanner, such as the scanner 2500 of FIG. 15, and theresults projected with a projector, which might be the projector in thesix-DOF scanner or in a six-DOF projector.

FIG. 18 shows an embodiment of a six-DOF projector 2700 used inconjunction with an optoelectronic system 2790. The optoelectronicsystem 2790 may be any device capable of measuring the six degrees offreedom of a six-DOF projector 2700. In an embodiment, theoptoelectronic system 2790 contains one or more cameras that viewilluminated light sources of retroreflectors on the six-DOF projector2700. By noting the relative positions of the light source images on theone or more cameras, the three degrees of orientational freedom arefound. Three additional degrees of freedom are found, for example, byusing a distance meter and two angular encoders to find the threedimensional coordinates of the retroreflector 2710. In anotherembodiment, the three degrees of orientational freedom are found bysending a beam of light through a vertex of a cube corner retroreflector2710 to a position detector, which might be a photosensitive array, todetermine two degrees of freedom and by sending a polarized beam oflight, which may be the same beam of light, through at least onepolarizing beam splitter to determine a third degree of freedom. In athird embodiment, the optoelectronic assembly 2790 sends a pattern oflight onto the six-DOF projector 2700. In this embodiment, the interfacecomponent 2712 includes a plurality of linear position detectors, whichmay be linear photosensitive arrays, to detect the pattern and from thisto determine the three degrees of orientational freedom of the six-DOFprojector 2700. Many other optoelectronic systems 2790 are possible fordetermine the six degrees of freedom of the six-DOF projector 2700, aswill be known to one of ordinary skill in the art. The six-DOF projector2700 includes a body 2714, one or more retroreflectors 2710, 2711, aprojector 2720, an optional electrical cable 2736, an optional battery2734, an interface component 2712, an identifier element 2739, actuatorbuttons 2716, an antenna 2738, and an electronics circuit board 2732.The optional electrical cable 2736, the optional battery 2734, theinterface component 2712, the identifier element 2739, the actuatorbuttons 2716, the antenna 2738, and the electronics circuit board 2732of FIG. 18 correspond to the retroreflector 2010, the optionalelectrical cable 2046, the optional battery 2044, the interfacecomponent 2012, the identifier element 2049, actuator buttons 2016, theantenna 2048, and the electronics circuit board 2042, respectively, inFIG. 14. The descriptions for these corresponding elements are the sameas discussed hereinabove and will not be repeated. Additionalretroreflectors, such as retroreflector 2711, may be added to the firstretroreflector 2710 to enable the laser tracker to track the six-DOFscanner from a variety of directions, thereby giving greater flexibilityin the directions to which light may be projected by the six-DOFprojector 2700.

Referring back to FIG. 15, we note that for the case in which thescanner light source 2520 serves as a projector for displaying a patternin addition to providing a light source for use in combination with thescanner camera 2530 (for determining the three dimensional coordinatesof the workpiece), other methods for finding the six degrees of freedomof the target 2500 can be used. Such methods may include the methodsdiscussed with reference to FIG. 18, even though not explicitly shown inFIG. 15.

FIGS. 17 and 18 are similar except that the six-DOF projector FIG. 18may use a wider range of six-DOF measurement methods than the six-DOFprojector of FIG. 17. All of the comments made about the applicationsfor the six-DOF projector 2600 also apply to the six-DOF projector 2700.

FIG. 19 shows an embodiment of a six-DOF sensor 4900 used in conjunctionwith an optoelectronic system 2790. The optoelectronic system 2790 maybe any device capable of measuring the six degrees of freedom of asix-DOF sensor 4900. In an embodiment, the optoelectronic system 2790contains one or more cameras that view illuminated light sources ofretroreflectors on the six-DOF sensor 4900. By noting the relativepositions of the light source images on the one or more cameras, thethree degrees of orientational freedom are found. Three additionaldegrees of freedom are found, for example, by using a distance meter andtwo angular encoders to find the three dimensional coordinates of theretroreflector 4910. In another embodiment, the three degrees oforientational freedom are found by sending a beam of light through avertex of a cube corner retroreflector 4910 to a position detector,which might be a photosensitive array, to determine two degrees offreedom and by sending a polarized beam of light, which may be the samebeam of light, through at least one polarizing beam splitter todetermine a third degree of freedom. In a third embodiment, theoptoelectronic assembly 2790 sends a pattern of light onto the six-DOFsensor 4900. In this embodiment, the interface component 4912 includes aplurality of linear position detectors, which may be linearphotosensitive arrays, to detect the pattern and from this to determinethe three degrees of orientational freedom of the six-DOF projector2700. Many other optoelectronic systems 2790 are possible for determinethe six degrees of freedom of the six-DOF projector 2700, as will beknown to one of ordinary skill in the art. The six-DOF sensor 4900includes a body 4914, one or more retroreflectors 4910, 4911, a sensor4920, an optional source 4950, an optional electrical cable 4936, anoptional battery 4934, an interface component 4912, an identifierelement 4939, actuator buttons 4916, an antenna 4938, and an electronicscircuit board 4932. The optional electrical cable 4936, the optionalbattery 4934, the interface component 4912, the identifier element 4939,the actuator buttons 4916, the antenna 4938, and the electronics circuitboard 4932 of FIG. 18 correspond to the retroreflector 2010, theoptional electrical cable 2046, the optional battery 2044, the interfacecomponent 2012, the identifier element 2049, actuator buttons 2016, theantenna 2048, and the electronics circuit board 2042, respectively, inFIG. 14. The descriptions for these corresponding elements are the sameas discussed hereinabove and will not be repeated. Additionalretroreflectors, such as retroreflector 4911, may be added to the firstretroreflector 4910 to enable the laser tracker to track the six-DOFscanner from a variety of directions, thereby giving greater flexibilityin the directions to which an object may be sensed by the six-DOF sensor4900.

The sensor 4920 may be of a variety of types. For example, it mayrespond to optical energy in the infrared region of the spectrum, thelight having wavelengths from 0.7 to 20 micrometers, thereby enablingdetermination of a temperature of an object surface at a point 4924. Thesensor 4920 is configured to collect infrared energy emitted by theobject 4960 over a field of view 4940, which is generally centered aboutan axis 4922. The three-dimensional coordinates of the point on theobject surface corresponding to the measured surface temperature may befound by projecting the axis 4922 onto the object 4960 and finding thepoint of intersection 4924. To determine the point of intersection, therelationship between the object frame of reference and the device(tracker) frame of reference needs to be known, Alternatively, therelationship between the object frame of reference and the six-DOFsensor frame of reference may be known since the relationship betweenthe tracker frame of reference and the sensor frame of reference isalready known. Alternatively, the relationship between the object frameof reference and the six-DOF sensor frame of reference may be knownsince the relationship between the tracker frame of reference and thesix-DOF sensor is already known from measurements performed by thetracker on the six-DOF sensor. One way to determine the relationshipbetween the object frame of reference and the tracker frame of referenceis to measure the three-dimensional coordinates of three points on thesurface of the object. By having information about the object inrelation to the three measured points, all points on the object of thesurface will be known. Information on the object in relation to thethree measured points may be obtained, for example, from CAD drawings orfrom previous measurements made by any type of coordinate measurementdevice.

Besides measuring emitted infrared energy, the electromagnetic spectrummay be measured (sensed) over a wide range of wavelengths, orequivalently frequencies. For example, electromagnetic energy may be inthe optical region and may include visible, ultraviolet, infrared, andterahertz regions. Some characteristics, such as the thermal energyemitted by the object according to the temperature of the object, areinherent in the properties of the object and do not require externalillumination. Other characteristics, such as the color of an object,depend on background illumination and the sensed results may changeaccording to the characteristics of the illumination, for example, inthe amount of optical power available in each of the wavelengths of theillumination. Measured optical characteristics may include optical powerreceived by an optical detector, and may integrate the energy a varietyof wavelengths to produce an electrical response according to theresponsivity of the optical detector at each wavelength.

In some cases, the illumination may be intentionally applied to theobject by a source 4950. If an experiment is being carried out in whichit is desired that the applied illumination be distinguished from thebackground illumination, the applied light may be modulated, forexample, by a sine wave or a square wave. A lock-in amplifier or similarmethod can then be used in conjunction with the optical detector in thesensor 4920 to extract just the applied light.

Other examples of the sensing of electromagnetic radiation by the sensor4940 include the sensing of X-rays at wavelengths shorter than thosepresent in ultraviolet light and the sensing of millimeter-wave,microwaves, RF wave, and so forth are examples of wavelengths longerthan those present in terahertz waves and other optical waves. X-raysmay be used to penetrate materials to obtain information about interiorcharacteristics of object, for example, the presence of defects or thepresence of more than one type of material. The source 4950 may be usedto emit X-rays to illuminate the object 4960. By moving the six-DOFsensor 4900 and observing the presence of a defect or material interfacefrom a plurality of views, it is possible to determine thethree-dimensional coordinates of the defect or material interface withinthe material. Furthermore, if a sensor 4940 is combined with a projectorsuch as the projector 2720 in FIGS. 17 and 18, a pattern may beprojected onto an object surface that indicates where repair work needsto be carried out to repair the defect.

In an embodiment, the source 4950 provides electromagnetic energy in theelectrical region of the spectrum—millimeter-wave, microwave, or RFwave. The waves from the source illuminate the object 4960, and thereflected or scattered waves are picked up by the sensor 4920. In anembodiment, the electrical waves are used to penetrate behind walls orother objects. For example, such a device might be used to detect thepresence of RFID tags. In this way, the six-DOF sensor 4900 may be usedto determine the position of RFID tags located throughout a factory.Other objects besides RFID tags may also be located. For example, asource of RF waves or microwaves such as a welding apparatus emittinghigh levels of broadband electromagnetic energy that is interfering withcomputers or other electrical devices may be located using a six-DOFscanner.

In an embodiment, the source 4950 provides ultrasonic waves and thesensor 4920 is an ultrasonic sensor. Ultrasonic sensors may have anadvantage over optical sensors when sensing clear objects, liquidlevels, or highly reflective or metallic surfaces. In a medical context,ultrasonic sensors may be used to localize the position of viewedfeatures in relation to a patient's body. The sensor 4920 may be achemical sensor configured to detect trace chemical constituents andprovide a chemical signature for the detected chemical constituents. Thesensor 4920 may be configured to sense the presence of radioactivedecay, thereby indicating whether an object poses a risk for humanexposure. The sensor 4920 may be configured to measure surface texturesuch as surface roughness, waviness, and lay. The sensor may be aprofilometer, an interferometer, a confocal microscope, a capacitancemeter, or similar device. A six-DOF scanner may also be used for measuresurface texture. Other object characteristics can be measured usingother types of sensors not mentioned hereinabove.

FIG. 19A shows an embodiment of a six-DOF sensor 4990 that is like thesix-DOF sensor 4900 of FIG. 19 except that the sensor 4922 of thesix-DOF sensor 4990 includes a lens 4923 and a photosensitive array4924. An emitted or reflected ray of energy 4925 from within a field ofview 4940 of the six-DOF sensor arises at a point 4926 on the objectsurface 4960, passes through a perspective center 4927 of sensor lens4923 to arrive at a point 4928 on the photosensitive array 4924. Asource 4950 may illuminate a region of the object surface 4960, therebyproducing a response on the photosensitive array. Each point isassociated with three-dimensional coordinates of the sensedcharacteristic on the object surface, each three-dimensional pointdetermined by the three orientational degrees of freedom, the threetranslational degrees of freedom, the geometry of the camera andprojector within the sensor assembly, and the position on thephotosensitive array corresponding to the point on the object surface.An example of sensor 4922 is a thermal array sensor that responds byproviding a temperature at a variety of pixels, each characteristicsensor value associated with a three-dimensional surface coordinate.

FIG. 20 is a flowchart illustrating steps 5000 in a method of measuringthree or more surface sets on an object surface with a coordinatemeasurement device and a target scanner, each of the three or moresurface sets being three-dimensional coordinates of a point on theobject surface in a device frame of reference, each surface setincluding three values, the device frame of reference being associatedwith the coordinate measurement device.

The step 5005 is to provide the target scanner with a body, a firstretroreflector, a projector, a camera, and a scanner processor, whereinthe first retroreflector, projector, and camera are rigidly affixed tothe body, and the target scanner is mechanically detached from thecoordinate measurement device. In this step, the projector includes asource pattern of light, the source pattern of light located on a sourceplane and including at least three non-collinear pattern elements, theprojector is configured to project the source pattern of light onto theobject to form an object pattern of light on the object, and each of theat least three non-collinear pattern elements correspond to at least onesurface set. Also in this step, the camera includes a camera lens and aphotosensitive array, the camera lens configured to image the objectpattern of light onto the photosensitive array as an image pattern oflight, the photosensitive array including camera pixels, thephotosensitive array configured to produce, for each camera pixel, acorresponding pixel digital value responsive to an amount of lightreceived by the camera pixel from the image pattern of light.

The step 5010 is to provide the coordinate measurement device, thecoordinate measurement device configured to measure a translational setand an orientational set, the translational set being values of threetranslational degrees of freedom of the target scanner in the deviceframe of reference and the orientational set being values of threeorientational degrees of freedom of the target scanner in the deviceframe of reference, the translational set and the orientational setbeing sufficient to define a position and orientation of the targetscanner in space, the coordinate measurement device configured to send afirst beam of light to the first retroreflector and to receive a secondbeam of light from the first retroreflector, the second beam of lightbeing a portion of the first beam of light, the coordinate measurementdevice including a device processor, the device processor configured todetermine the orientational set and the translational set, thetranslational set based at least in part on the second beam of light.Also in this step, the scanner processor and the device processor arejointly configured to determine the three or more surface sets, each ofthe surface sets based at least in part on the translational set, theorientational set, and the pixel digital values.

The step 5015 is to select the source pattern of light.

The step 5020 is to project the source pattern of light onto the objectto produce the object pattern of light.

The step 5025 is to image the object pattern of light onto thephotosensitive array to obtain the image pattern of light.

The step 5030 is to obtain the pixel digital values for the imagepattern of light.

The step 5035 is to send the first beam of light from the coordinatemeasurement device to the first retroreflector.

The step 5040 is to receive the second beam of light from the firstretroreflector.

The step 5045 is to measure the orientational set and the translationalset, the translational set based at least in part on the second beam oflight.

The step 5050 is to determine the surface sets corresponding to each ofthe at least three non-collinear pattern elements.

The step 5055 is to save the surface sets. The method 5000 concludeswith marker A.

FIG. 21 is a flowchart illustrating steps 5100 in a method that followson marker A of FIG. 20.

A step 5105 is to touch the tactile probe to the object surface.

A step 5110 is to measure the translational set and the orientationalset.

A step 5115 is to determine a second surface set based at least in parton the translational set and the orientational set.

FIG. 22 is a flowchart illustrating steps 5200 in a method that followson marker A of FIG. 20. A step 5205 is to evaluate the surface sets. Astep 5210 is to indicate to a user that a region of the object surfaceis to be measured with the tactile probe based at least in part on theevaluated surface sets.

FIG. 23 is a flowchart illustrating steps 5300 in a method that followson marker A of FIG. 20. A step 5305 is to incorporate a pattern into thefirst retroreflector. A step 5310 is to provide a second optical systemincluding a second lens and a second photosensitive array, the secondlens configured to form a second image of at least a portion of thefirst retroreflector on the second photosensitive array. A step 5315 isto convert the second image into a second digital data set. The step5320 is to calculate the orientational set based at least in part on thesecond digital data set.

FIG. 24 is a flowchart illustrating steps 5400 in a method of measuringwith a coordinate measurement device and a target sensor a sensecharacteristic and a surface set associated with the sensecharacteristic, the surface set being three-dimensional coordinates of apoint on the object surface in a device frame of reference, each surfaceset including three values, the device frame of reference beingassociated with the coordinate measurement device.

The step 5405 is to provide the target sensor having a body, a firstretroreflector, a sensor, and a sensor processor, wherein the firstretroreflector and the sensor are rigidly affixed to the body, and thetarget sensor is mechanically detached from the coordinate measurementdevice, the target sensor configured to measure the sensecharacteristic, the sense characteristic being a value associated with aquantity measured by the sensor.

The step 5410 is to provide the coordinate measurement device, thecoordinate measurement device configured to measure a translational setand an orientational set, the translational set being values of threetranslational degrees of freedom of the target sensor in the deviceframe of reference and the orientational set being values of threeorientational degrees of freedom of the target sensor in the deviceframe of reference, the translational set and the orientational setbeing sufficient to define a position and orientation of the targetsensor in space, the coordinate measurement device configured to send afirst beam of light to the first retroreflector and to receive a secondbeam of light from the first retroreflector, the second beam of lightbeing a portion of the first beam of light, the coordinate measurementdevice including a device processor, the device processor configured todetermine the orientational set and the translational set, thetranslation set based at least in part on the second beam of light,wherein the sensor processor and the device processor are jointlyconfigured to determine the sense characteristic and the surface set,the surface set based at least in part on the translational set and theorientational set.

The step 5415 is to send the first beam of light from the coordinatemeasurement device to the first retroreflector.

The step 5420 is to receive the second beam of light from the firstretroreflector.

The step 5425 is to measure the orientational set and the translationalset, the translational set based at least in part on the second beam oflight.

The step 5430 is to determine the surface set.

The step 5435 is to sense the sense characteristic.

The step 5440 is to save the surface set and the sense characteristic.The method 5400 concludes at a marker B.

FIG. 25 is a flowchart illustrating steps 5500 in a method that beginswith the marker B of FIG. 24. A step 5505 is to incorporate a patterninto the first retroreflector.

A step 5510 is to provide an optical system including a second lens anda second photosensitive array, the second lens configured to form asecond image of at least a portion of the patterned retroreflector onthe second photosensitive array.

A step 5515 is to convert the second image into a second digital dataset.

The step 5520 is to calculate the orientational set based at least inpart on the second digital data set.

FIG. 26 is a flowchart illustrating steps 5600 in a method of conveyingfirst information to a user of a coordinate measurement device byprojecting a first pattern with a first target projector.

The step 5605 is to provide the first target projector having atarget-projector frame of reference and to include a body, a firstretroreflector, and a projector, wherein the first retroreflector andprojector are rigidly affixed to the body, the first target projectormechanically detached from the coordinate measurement device, theprojector configured to project a pattern of light in two dimensions,the pattern of light forming a three-dimensional pattern of light whenintercepted by a three-dimensional object.

The step 5610 is to provide the coordinate measurement device having adevice frame of reference, the coordinate measurement device configuredto measure a translational set and an orientational set, thetranslational set being values of three translational degrees of freedomof the first target projector in the device frame of reference and theorientational set being values of three orientational degrees of freedomof the first target projector in the device frame of reference, thetranslational set and the orientational set being sufficient to define aposition and orientation of the first target projector in space, thecoordinate measurement device configured to send a first beam of lightto the first retroreflector and to receive a second beam of light fromthe first retroreflector, the second beam of light being a portion ofthe first beam of light, the coordinate measurement device including adevice processor configured to determine the orientation set and thetranslational set, the translational set based at least in part on thesecond beam of light.

The step 5615 is to send the first beam of light from the coordinatemeasurement device to the first retroreflector.

The step 5620 is to receive the second beam of light from the firstretroreflector.

The step 5625 is to measure the orientational set and translational set,the translational set based at least in part on the second beam oflight.

The step 5630 is to select the first information to be conveyed, thefirst information selected from the group consisting of a position onthe object, a plurality of positions on the object, a directionindicated by a moving pattern, a message that includes one or moresymbols or alphanumeric characters, a hidden feature, a measured objectcharacteristic, a modeled characteristic, a magnified representation ofsurface characteristics, a pattern having meaning according to a rule,and combinations thereof.

The step 5635 is to determine the first pattern of light correspondingto the first information.

The step 5640 is to store the first pattern.

The step 5645 is to project from the projector the first pattern oflight onto the object based at least in part on the translational setand the orientational set. The method 5600 concludes at a marker C.

FIG. 27 a flowchart illustrating steps 5700 in a method that begins withthe marker C of FIG. 26. The step 5705 is to measure with the coordinatemeasurement device while the first target projector continues to projectthe first pattern of light onto the object.

FIG. 28 is a flowchart illustrating steps 5800 in a method that beginswith the marker C of FIG. 26. The step 5805 is to provide a secondtarget projector having a third retroreflector. The step 5810 is to sendthe first beam of light to the third retroreflector. The step 5815 is toreturn the second beam of light from the third retroreflector to thecoordinate measurement device.

FIG. 29 is a flowchart illustrating steps 5900 in a method that beginswith a marker C of FIG. 26. The step 5905 is to incorporate a patterninto the first retroreflector. The step 5910 is to provide a secondoptical system. The step 5915 is to convert the second image into asecond digital data set. The step 5920 is to calculate the orientationalset based at least in part on the second digital data set.

FIG. 30 is a flowchart illustrating steps 6000 in a method that beginswith the marker C of FIG. 26. The step 6005 is to provide the firsttarget projector with a speaker. The step 6010 is to select secondinformation to be conveyed. The step 6015 is to determine a first audiomessage corresponding to the second information. The step 6020 is toissue the first audio message from the speaker.

FIG. 31 is a flowchart illustrating steps 6100 to measure a plurality ofsurface sets on an object surface with a coordinate measurement deviceand a target scanner, each of the surface sets being three-dimensionalcoordinates of a point on the object surface in a device frame ofreference, each surface set including three values, the device frame ofreference being associated with the coordinate measurement device.

The step 6105 is to provide the target scanner having a body, a firstretroreflector incorporating a pattern, a projector, a camera, and ascanner processor, wherein the first retroreflector, projector, andcamera are rigidly affixed to the body, and the target scanner ismechanically detached from the coordinate measurement device, whereinthe projector includes a source pattern of light, the source pattern oflight located on a source plane and including a plurality of collinearpattern elements, the projector configured to project the source patternof light onto the object to form an object pattern of light on theobject, each of the pattern elements corresponding to at least onesurface set, wherein the camera includes a first lens and a firstphotosensitive array, the first lens configured to image the objectpattern of light onto the first photosensitive array as an image patternof light, the first photosensitive array including camera pixels, thefirst photosensitive array configured to produce, for each camera pixel,a corresponding pixel digital value responsive to an amount of lightreceived by the camera pixel from the image pattern of light.

The step 6110 is to provide the coordinate measurement device, thecoordinate measurement device configured to measure a translational setand an orientational set, the translational set being values of threetranslational degrees of freedom of the target scanner in the deviceframe of reference and the orientational set being values of threeorientational degrees of freedom of the target scanner in the deviceframe of reference, the translational set and the orientational setbeing sufficient to define a position and orientation of the targetscanner in space, the coordinate measurement device configured to send afirst beam of light to the first retroreflector and to receive a secondbeam of light from the first retroreflector, the second beam of lightbeing a portion of the first beam of light, the coordinate measurementdevice including a device processor, the device processor configured todetermine the orientational set and the translational set, theorientational set and the translational set based at least in part onthe second beam of light, the coordinate measurement device including asecond optical system, the second optical system including a second lensand a second photosensitive array, the second lens configured to form asecond image of at least a portion of the first retroreflector on thesecond photosensitive array, the coordinate measurement deviceconfigured to convert the second image into a second digital data setand to calculate the orientational set based at least in part on thesecond digital data set, wherein the scanner processor and the deviceprocessor are jointly configured to determine the plurality of surfacesets, each of the surface sets based at least in part on thetranslational set, the orientational set, and the pixel digital values.

The step 6115 is to select the source pattern of light.

The step 6120 is to project the source pattern of light onto the objectto produce the object pattern of light.

The step 6125 is to image the object pattern of light onto thephotosensitive array to obtain the image pattern of light.

The step 6130 is to obtain the pixel digital values for the imagepattern of light.

The step 6135 is to send the first beam of light from the coordinatemeasurement device to the first retroreflector.

The step 6140 is to receive the second beam of light from the firstretroreflector.

The step 6145 is to measure the orientational set and the translationalset based at least in part on the second beam of light.

The step 6150 is to determine the surface sets corresponding to theplurality of collinear pattern elements.

The step 6155 is to save the surface sets.

FIG. 32 is a flowchart illustrating steps 6200 to measure a plurality ofsurface sets on an object surface with a coordinate measurement deviceand a target scanner, each of the surface sets being three-dimensionalcoordinates of a point on the object surface in a device frame ofreference, each surface set including three values, the device frame ofreference being associated with the coordinate measurement device.

The step 6205 is to provide a target scanner having a body, a firstretroreflector, a projector, a camera, and a scanner processor, whereinthe first retroreflector, projector, and camera are rigidly affixed tothe body, and the target scanner is mechanically detached from thecoordinate measurement device, wherein the projector includes a sourcepattern of light, the source pattern of light located on a source planeand including a plurality of collinear pattern elements, the projectorconfigured to project the source pattern of light onto the object toform an object pattern of light on the object, each of the patternelements corresponding to at least one surface set, wherein the cameraincludes a first lens and a first photosensitive array, the first lensconfigured to image the object pattern of light onto the firstphotosensitive array as an image pattern of light, the firstphotosensitive array including camera pixels, the first photosensitivearray configured to produce, for each camera pixel, a correspondingpixel digital value responsive to an amount of light received by thecamera pixel from the image pattern of light.

The step 6210 is to provide the coordinate measurement device, thecoordinate measurement device configured to measure a translational setand an orientational set, the translational set being values of threetranslational degrees of freedom of the target scanner in the deviceframe of reference and the orientational set being values of threeorientational degrees of freedom of the target scanner in the deviceframe of reference, the translational set and the orientational setbeing sufficient to define a position and orientation of the targetscanner in space, the coordinate measurement device configured to send afirst beam of light to the first retroreflector and to receive a secondbeam of light from the first retroreflector, the second beam of lightbeing a portion of the first beam of light, the coordinate measurementdevice including a device processor, the device processor configured todetermine the orientational set and the translational set, thetranslational set based at least in part on the second beam of light,wherein the scanner processor and the device processor are jointlyconfigured to determine the plurality of surface sets, each of thesurface sets based at least in part on the translational set, theorientational set, and the pixel digital values.

The step 6215 is to select the source pattern of light.

The step 6220 is to project the source pattern of light onto the objectto produce the object pattern of light.

The step 6225 is to image the object pattern of light onto thephotosensitive array to obtain the image pattern of light.

The step 6230 is to obtain the pixel digital values for the imagepattern of light.

The step 6235 is to send the first beam of light from the coordinatemeasurement device to the first retroreflector.

The step 6240 is to receive the second beam of light from the firstretroreflector.

The step 6245 is to measure the orientational set and the translationalset, the translational set based at least in part on the second beam oflight.

The step 6250 is to determine the surface sets corresponding to theplurality of collinear pattern elements.

The step 6255 is to save the surface sets.

While the invention has been described with reference to exampleembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include all embodiments falling within the scope of the appendedclaims. Moreover, the use of the terms first, second, etc. do not denoteany order or importance, but rather the terms first, second, etc. areused to distinguish one element from another. Furthermore, the use ofthe terms a, an, etc. do not denote a limitation of quantity, but ratherdenote the presence of at least one of the referenced item.

1. A method of conveying first information to a user of a coordinatemeasurement device by projecting a first pattern with a first targetprojector, the method comprising steps of: providing the first targetprojector having a target-projector frame of reference and including abody, a first retroreflector, and a projector, wherein the firstretroreflector and projector are rigidly affixed to the body, the firsttarget projector mechanically detached from the coordinate measurementdevice, the projector configured to project a pattern of light in twodimensions, the pattern of light forming a three-dimensional pattern oflight when intercepted by a three-dimensional object, providing thecoordinate measurement device having a device frame of reference, thecoordinate measurement device configured to measure a translational setand an orientational set, the translational set being values of threetranslational degrees of freedom of the first target projector in thedevice frame of reference and the orientational set being values ofthree orientational degrees of freedom of the first target projector inthe device frame of reference, the translational set and theorientational set being sufficient to define a position and orientationof the first target projector in space, the coordinate measurementdevice configured to send a first beam of light to the firstretroreflector and to receive a second beam of light from the firstretroreflector, the second beam of light being a portion of the firstbeam of light, the coordinate measurement device including a deviceprocessor configured to determine the orientation set and thetranslational set, the translational set based at least in part on thesecond beam of light; sending the first beam of light from thecoordinate measurement device to the first retroreflector; receiving thesecond beam of light from the first retroreflector; measuring theorientational set and translational set, the translational set based atleast in part on the second beam of light; selecting the firstinformation to be conveyed, the first information selected from thegroup consisting of a position on the object, a plurality of positionson the object, a direction indicated by a moving pattern, a message thatincludes one or more symbols or alphanumeric characters, a hiddenfeature, a measured object characteristic, a modeled characteristic, amagnified representation of surface characteristics, a pattern havingmeaning according to a rule, and combinations thereof; determining thefirst pattern of light corresponding to the first information; storingthe first pattern; and projecting from the projector the first patternof light onto the object based at least in part on the translational setand the orientational set.
 2. The method of claim 1, wherein the step ofproviding the coordinate measurement device further includes providingthe coordinate measurement device including a first motor, a secondmotor, a first angle measuring device, a second angle measuring device,a distance meter, a position detector, a control system, and a deviceprocessor, the first motor and the second motor together configured todirect the first beam of light to a first direction, the first directiondetermined by a first angle of rotation about a first axis and a secondangle of rotation about a second axis, the first angle of rotationproduced by the first motor and the second angle of rotation produced bythe second motor, the first angle measuring device configured to measurethe first angle of rotation and the second angle measuring deviceconfigured to measure the second angle of rotation, the distance meterconfigured to measure a first distance from the coordinate measurementdevice to the first retroreflector, the position detector configured toreceive a second portion of the second beam of light and to send a firstsignal to the control system, the first signal produced in response to aposition of the second portion on the position detector, the controlsystem configured to send a second signal to the first motor, to send athird signal to the second motor, and to adjust the first direction ofthe first beam of light to the position in space of the firstretroreflector, the second signal and the third signal based at least inpart on the first signal, the device processor configured to determinethe translational set and the orientational set, the translational setbased at least in part on the first distance, the first angle ofrotation, and the second angle of rotation.
 3. The method of claim 1,wherein the step of determining the first pattern of light furtherincludes a step of determining a transformation relationship between anobject frame of reference for the object and a frame of referenceselected from the group consisting of the device frame of reference andthe target-projector frame of reference.
 4. The method of claim 3,wherein the step of determining the first pattern of light furtherincludes measuring with the coordinate measurement device threedimensional coordinates of at least three non-collinear points on theobject.
 5. The method of claim 3, wherein: the step of selecting thefirst information to be conveyed further includes selecting a firstposition on the object where an assembly operation is to be performed ora first plurality of positions on the object where an assembly operationis to be performed; and the step of projecting from the projector thefirst pattern further includes projecting the first pattern to the firstposition or the first plurality of positions.
 6. The method of claim 5,wherein, in the step of selecting the first information to be conveyed,the assembly operation to be performed is selected from the groupconsisting of drilling, scribing, removing surface material, addingsurface material, attaching a component, applying adhesive, applying acoating, applying a label, cleaning, and combinations thereof.
 7. Themethod of claim 3, wherein: the step of selecting the first informationto be conveyed further includes directing measurements with thedimensional measurement device; and the step of projecting from theprojector the first pattern further includes projecting a pattern oflight in the direction at which a dimensional measurement is to be made.8. The method of claim 1, wherein the step of selecting the firstinformation to be conveyed further includes selecting a pattern havingmeaning according to a rule from among a plurality of rules, theplurality of rules configured to be available to the user in written ordisplayed form.
 9. The method of claim 3, wherein: the step of selectingthe first information to be conveyed further includes selecting a hiddenfeature, the hidden feature obtained from drawings or measured data; andthe step of projecting from the projector the first pattern furtherincludes projecting the first pattern over a portion of a first area,the first area being an area of the object for which the hidden featureinformation is available.
 10. The method of claim 3, wherein: the stepof selecting the first information to be conveyed further includesselecting measured object characteristics that include measured error,the measured error taken as the difference between measured dimensionalvalues and nominal or specified dimensional values; and the step ofprojecting from the projector the first pattern further includesprojecting the first pattern over a portion of a first area, the firstarea being an area of the object for which the measured objectcharacteristics are available.
 11. The method of claim 3, wherein: thestep of selecting the first information to be conveyed further includesselecting measured object characteristics, the measured objectcharacteristic selected from the group consisting of temperature values,ultrasound values, microwave values, millimeter-wave values, X-rayvalues, radiological values, chemical sensing values, and combinationsthereof; and the step of projecting from the projector the first patternfurther includes projecting the first pattern over a portion of a firstarea, the first area being an area of the object for which the measuredobject characteristics are available.
 12. The method of claim 3,wherein: the step of selecting the first information to be conveyedfurther includes selecting modeled characteristics, the modeledcharacteristics including values obtained from finite-element analysis;and the step of projecting from the projector the first pattern onto theobject further includes projecting the first pattern over a portion of afirst area, the first area being an area of the object for which themodeled characteristics are available.
 13. The method of claim 1,wherein the step of selecting the first information to be conveyedincludes selecting the first information based at least in part on agesture given by the user and detected and interpreted by the coordinatemeasurement device or by a computer attached to the coordinatemeasurement device.
 14. The method of claim 1, wherein the step ofproviding the first target projector further includes providing afixture rigidly attached to the body, the fixture stationary withrespect to the device frame of reference.
 15. The method of claim 14,wherein the step of projecting from the projector the first pattern oflight onto the object further includes continuing to project the firstpattern of light onto the object when the coordinate measurement deviceno longer sends the first beam of light to the first retroreflector. 16.The method of claim 15, further including a step of measuring with thecoordinate measurement device while the first target projector continuesto project the first pattern of light onto the object.
 17. The method ofclaim 15, further including: providing a second target projector havinga third retroreflector; sending the first beam of light to the thirdretroreflector; and returning the second beam of light from the thirdretroreflector to the coordinate measurement device.
 18. The method ofclaim 1, wherein the step of providing the first target projectorfurther includes providing a movable carrier, the first target projectorattached to the movable carrier.
 19. The method of claim 18, wherein, inthe step of providing the first target projector, the movable carrier isa robot.
 20. The method of claim 3, wherein, in the step of providingthe coordinate measurement device and the first target projector, thefirst target projector further includes a tactile probe configured tomeasure three-dimensional coordinates of a first point on a surface ofthe object, the measured three-dimensional coordinates based at least inpart on the translational set and the orientational set.
 21. The methodof claim 20, wherein the step of projecting from the projector the firstpattern of light onto the object further includes indicating a positionto be measured on the object surface, the indication given by projectingthe first pattern of light onto the object surface.
 22. The method ofclaim 1, further including steps of: incorporating a pattern into thefirst retroreflector; providing a second optical system including asecond lens and a second photosensitive array, the second lensconfigured to form a second image of at least a portion of the firstretroreflector on the second photosensitive array; converting the secondimage into a second digital data set; and calculating the orientationalset based at least in part on the second digital data set.
 23. Themethod of claim 1, further including steps of: providing the firsttarget projector with a speaker, the speaker configured to give audiomessages; selecting second information to be conveyed; determining afirst audio message corresponding to the second information; and issuingthe first audio message from the speaker.
 24. The method of claim 1,wherein: the step of providing the first target projector furtherincludes providing a second retroreflector rigidly attached to the body;and the step of measuring the translational set and the orientationalset with the coordinate measurement device further includes rotating thefirst target projector to acquire the second retroreflector with thefirst beam of light from the coordinate measurement device.
 25. Themethod of claim 3, wherein the step of providing the first targetprojector further includes providing a handle on the first targetprojector.
 26. The method of claim 1, wherein: the step of selecting thefirst information to be conveyed further includes selecting a magnifiedrepresentation of surface characteristics, the magnified representationof surface characteristics obtained from measurements; and the step ofprojecting from the projector the first pattern onto the object furtherincludes projecting the first pattern over a portion of a first area,the first area being an area of the object for which the magnifiedrepresentation of surface characteristics is available.